Performance-Based Analysis of Geometric Design of Highways and Streets (2014)

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61 C H A P T E R 6 6.1 Introduction These project examples are intended to help users apply the concepts, models, and perfor- mance evaluation framework element presented in Chapters 1 through 5. The project examples are based on a variety of specific projects, amalgams of projects, or project considerations that can be commonly found in practice. All roadway names and locations have been fictionalized and the key project elements emphasized to support and promote the principles of performance-based analysis of geometric design. Each project example includes authors’ notes to provide background or insights to the user as they work through each project example. The project examples are unique and offer independent value and utility. They represent a range of projects containing fairly common scenarios potentially faced by practitioners. Some of the project examples have been adopted and modified from actual projects that have integrated performance-based analysis into design decisions and/or could have benefited from incorporating performance-based analysis. Other project examples were created to illustrate the performance-based analysis process and communicate key learning objectives. In each project example, the names are changed and do not reflect the actual names of the facilities or agencies. While numbered from 1 through 6, users do not need to review the project examples sequen- tially. Doing so will help reinforce the fundamental performance-based model, report concept, and the performance-based model application framework. Following the project examples sequentially will provide repetition of the framework via a variety of project applications. Review- ing the project examples sequentially reinforces the principles of performance-based evaluations within a variety of unique applications. This may help the user apply the principles and models in a way that most appropriately meets individual project context and design situations. Users may also find the project examples a useful resource for recalling and applying specific performance-based tools and methods for a specific project type. For example, Project Exam- ple 6 considers a new interchange being evaluated on a highway. Project Example 3 presents a corridor evaluation where intended project outcomes include retrofitting an existing auto- oriented urban arterial to incorporate complete street attributes. The design solutions consid- erations focus on alternative street cross sections and the associated performance evaluation of the geometric choices of various alternatives. Users may also find value in focusing on a project example with similar qualities and characteristics as their own project. The project examples illustrate how the framework can be applied to projects within various stages of development and in a variety of contexts. Exhibit 6-1 summarizes the variety of project types, development stages, performance categories, and sites presented in the project examples. Exhibit 6-2 illustrates the basic framework for applying performance-based analysis of geo- metric design of highways and streets. Sections 5.1 through 5.4 in Chapter 5 provided supporting Project Examples

62 Performance-Based Analysis of Geometric Design of Highways and Streets Project Example Site Area and Facility Type Project Development Stage Performance Categories Project Type 1 US-21/Sanderson Road—Rural Collector (Two-Lane Highway) Alternatives Identification and Evaluation Safety Intersection—Consider alternative intersection control to improve safety. 2 Richter Pass Road—Rural Collector Preliminary Design Safety Mobility Segment—Consider alternative horizontal curve radii to improve safety while minimizing costs and maintaining appropriate speed. 3 Cascade Avenue—Suburban/ Urban Arterial Preliminary Design Safety Mobility Reliability Accessibility Quality of Service Corridor—Retrofitting an existing auto-oriented urban arterial to incorporate complete street attributes. Focus on alternative street cross sections. 4 SR-4—Rural Collector Preliminary Design Safety Reliability Quality of Service Segment—Consider alternative shoulder widths and sideslopes to minimize impact to an environmentally sensitive area. 5 27th Avenue—Urban Minor Arterial Alternatives Identification and Evaluation Quality of Service Safety Accessibility Segment—Alignment and cross- section considerations for new urban minor arterial being constructed to entice employers to a newly zoned industrial area. 6 US-6/Stonebrook Road—Rural Interchange Alternatives Identification and Evaluation Safety Mobility Interchange • Converting an at-grade rural intersection to a grade- separated interchange. • Focus on selecting the appropriate interchange form and location (e.g., spacing considerations). Exhibit 6-1. Summary of project examples. Exhibit 6-2. Performance-based analysis application framework.

Project Examples 63 information regarding the actions and considerations within each stage of the framework. Chap- ter 3 provided an overview of project performance categories and associated performance mea- sures that might be used in evaluating project solutions. Chapter 4 summarized the relationships between design elements and performance, identified possible performance tradeoffs, and pre- sented resources and tools that can be used to analyze a given design decision’s impact on per- formance measures. The six project examples within this chapter follow the process framework and steps shown in Exhibit 6-2. 6.2 Project Example 1: US-21/Sanderson Road Intersection Authors’ Note: Project Example 1 illustrates how performance-based analysis can be integrated into the alternatives identification and evaluation stage of an intersection project located on a rural, two-lane highway (i.e., rural arterial). The intended outcome of the project is improved safety. The project example focuses on safety as the performance category of interest and uses expected crash frequency as the primary performance metric, drawing on information in Section 4.4.4. The learning objectives of this project example include the following: • Illustrate the process of applying performance-based analysis • Demonstrate the use of resources beyond typical design manuals within the project development process • Illustrate how a financial feasibility assessment can inform project selection 6.2.1 Project Initiation 6.2.1.1 Project Context Authors’ Note: Using the considerations noted in Section 5.2.1, we are able to identify key characteristics of the project context that are likely to help inform the intended project outcomes, performance categories, and performance measures we will use to develop and evaluate potential solutions. The following summary of the project context sets the founda- tion for the remaining activities within the performance-based analysis framework. As will be discussed, a key motivation for this project is to improve highway safety while also improving wayfinding. The US-21/Sanderson Road intersection is located on a rural, two-lane highway (US-21). It is a two-way stop-controlled intersection serving as the primary entrance to a tribal reservation. The US-21 highway is a regional east-west connection through a rural, agricultural area; the surrounding land uses are a mixture of agricultural land, undeveloped lands, wetlands, and low- density residential. The highway is adjacent to the tribal land, providing the primary access from the tribal land to other small communities in the area. The average annual daily traffic (AADT) is approximately 7,700 vehicles per day (vpd). In the vicinity of the project intersection, the posted speed is 55 mph and the 85th percentile speed is 58 mph. There is limited to no pedestrian or bicycle activity along the corridor or at the intersection. The intersection operational level of service is LOS B, indicating little to no delay for motorists traveling through the intersection. Over the past 5 years, there were several fatal and serious injury crashes at the US-21/Sanderson Road intersection. Considering total crashes, 55% were angle or turning crashes and 26% were rear-end crashes. The most commonly cited contributing factors were failure to yield right-of- way (26% of crashes) and excessive speed (16% of crashes). Incremental solutions were applied to the intersection to improve safety—these included adding illumination as well as left-turn and right-turn lanes on US-21.

64 Performance-Based Analysis of Geometric Design of Highways and Streets 6.2.1.2 Intended Project Outcomes Authors’ Note: The following summarizes the key information related to whom the project is intended to serve, what the project is intended to achieve (i.e., intended project outcome), the appli- cable project performance category (or categories), and the applicable performance measures. Section 3.1 provides guidance and anecdotal examples of how to identify whom the project is intended to serve and what the project is intended to achieve. Sections 3.2 and 3.3 describe the overarching relationship and differences between defining project performance and geometric design performance. In this project example, the two are relatively closely aligned as both are focused on improving safety at the study intersection. In addition to improving safety, the tribe also has broader project interests: improving wayfinding to their tribal village and casino as well as creating the opportunity for more of a gateway treatment to their community. To inform the summary presented in this subsection of the intended project outcomes, we also used the information in Section 5.2.2 (which provides specific considerations for identifying the intended project outcomes), corresponding performance categories, and supporting performance measures. We used Section 4.4.5 to help select the performance measure: expected crash frequency and crash severity. The continued severe crashes at the US-21/Sanderson Road intersection motivated the tribe and the state department of transportation (DOT) to initiate this study to identify additional safety projects. The tribal community would like those projects to reduce the number and sever- ity of crashes as well as emphasize and enhance the intersection as the gateway to the community. The intersection modifications will need to accommodate a full range of motorized vehicles— agricultural equipment, logging trucks, and passenger vehicles of local residents and visitors. The primary performance category of interest is safety for the full range of road users just noted. From a geometric design perspective, the primary project category is safety and the per- formance measures are reducing the number and severity of intersection crashes. As potential solutions are developed, elements such as wayfinding and gateway treatments will be considered qualitatively. As will be discussed, some potential solutions may lend themselves more easily to adding signs, landscaping, and other similar features to emphasize the intersection as the gate- way to the tribal land. The geometric design decisions related to each potential solution will be driven more by how they influence potential crash frequency, crash severity, and/or speed as a key influencing factor to crash severity. 6.2.2 Concept Development 6.2.2.1 Geometric Influences Authors’ Note: We used the information presented in Section 5.3 and specifically Sec- tion 5.3.1 for guidance on how to approach identifying the geometric influences for the project. We used Section 4.4 to help inform, at a more detailed level, the specific geometric characteris- tics likely related to the key project performance measures. As a precursor to developing specific solutions for the US-21/Sanderson Road intersec- tion, the project team identified the design elements that have been documented to influ- ence crash frequency, crash severity, and other characteristics related to either frequency or severity of crashes—such as speed as it relates to crash severity or intersection visibility as it relates to frequency and severity of crashes. Exhibit 6-3 summarizes the design elements related to crash frequency and/or severity. Guidance for identifying the design elements that influence or are influenced by a given perfor- mance measure can be found in Section 4.4.

Project Examples 65 Identifying the design elements with the potential to influence crash frequency and severity serves as a starting place for brainstorming and exploring potential solutions. For example, there may be types of solutions that form a single alternative or a solution set that could be common across each alternative. In the case of identifying solutions for the US-21/Sanderson Road inter- section, the project team identified the following groupings of alternatives to explore: • Alternative intersection control • Advance signing and pavement markings • Changes in roadway cross-sectional features As will be seen later in the project example, elements of the advance signing and pavement marking treatments and changes in roadway cross section were transferable across the inter- section control alternatives. The added value of this approach was to be able to focus on incor- porating a full range of design elements most likely to improve intersection safety. 6.2.2.2 Potential Solutions Authors’ Note: Section 5.3.2 provides useful information and considerations for how to develop potential solutions given the specific project context, intended outcomes, performance measures, and influential geometric elements. In developing the specific potential solutions, the project team considered the three groups of alternatives noted above in concert with the information available regarding the prevailing crash types, contributing factors to crashes, mix of roadway users, existing roadway features, and surrounding land uses. Resources Used to Develop Solutions. The prevailing crash types at this intersection were turning and angle crashes. The primary contributing factors cited were failure to yield and exces- sive speed. Based on the desire to emphasize Sanderson Road as the entrance to the tribal land, the project team identified potential intersection configurations to make the intersection more Performance Target Related Design Elements Related Design Considerations Reduce Total Number of Crashes; Reduce Severity of Crashes Intersection Control Two-Way Stop • • All-Way Stop • Traffic Signal • Roundabout Intersection Design Features • Left-Turn Lanes • Right-Turn Lanes • Presence of Lighting • Visibility of Intersection Increase Intersection Awareness/Visibility Cross-Sectional Elements on Intersection Approach • Lane Width • Rumble Strips • Median (painted or splitter island type) Decrease Vehicle Speed on Intersection Approach Cross-Sectional Elements on Intersection Approach • Lane Width • Rumble Strips • Median (painted or splitter island type) Alignment on Intersection Approach • Roadway Curvature • Sight Distance • Advance Signing Exhibit 6-3. Design elements related to crash frequency and/or severity.

66 Performance-Based Analysis of Geometric Design of Highways and Streets visible and more clearly identifiable as the main intersection to access the tribal land. This project considered the following: • Implementing lane narrowing—pavement markings and rumble strips consistent with FHWA publications on low-cost treatment (see reference below) • Constructing a single-lane roundabout • Installing a traffic signal • Implementing specific wayfinding signs and landscaping as gateway treatments Given the context of the intersection and the potential solutions under consideration, the project team used the following resources to develop specific solutions concepts: • AASHTO’s A Policy on Geometric Design of Highways and Streets (1) • NCHRP Report 672: Roundabouts: An Informational Guide, Second Edition (2) • FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3) • NCHRP Report 613: Guidelines for the Selection of Speed Reduction Treatments on High- Speed Intersections (4) Solution Development. Using the previously listed resources, the project team developed functional designs of the potential alternatives to initially evaluate the feasibility and potential effectiveness of each concept. The following paragraphs discuss and illustrate this process and the considerations involved in developing the single-lane roundabout and traffic signal concepts. Exhibit 6-4 illustrates a hand-sketched functional design of a single-lane roundabout alterna- tive. The design is in scaled, sketch form [versus computer-assisted design (CAD)] and provides sufficient detail and information to assess the potential performance of this intersection form and to compare this roundabout treatment with other intersection forms. The exhibit also notes roadway approach treatments or welcome sign and other enhanced wayfinding as additional elements augmenting intersection design solutions. The enhanced Exhibit 6-4. Roundabout alternative for US-21/Sanderson Road.

Project Examples 67 wayfinding and related additional elements are an example of solution types that could be trans- ferable across broader alternatives to help achieve project goals. The design decisions reflected in Exhibit 6-4 include the following: • Appropriate size (e.g., inscribed circle diameter) of the roundabout given the posted speed on US-21, design vehicles, and anticipated turning-movement volumes • Number of entry and exit lanes on each approach given the anticipated turning-movement volumes • Entry and exit curve radii given the design vehicles and estimated entry, circulating, and exit- ing vehicle speeds • Appropriate length of the splitter islands on US-21 to help make the intersection visible and support appropriate speed reduction from the roadway segment to the roundabout entry These design considerations and others are more comprehensively described for roundabout intersections in NCHRP Report 672: Roundabout Informational Guide, Second Edition (2). This document highlights a performance-based approach to assess vehicle speeds, design vehicles service, and ability to accommodate non-motorized travelers. The key reasons for considering the previously noted roundabout design elements in the alter- natives development and evaluation stage is to determine their impact on performance (safety and operations), assess the feasibility of the roundabout, and estimate potential right-of-way impacts of the alternative. Exhibit 6-5 illustrates a similar level of functional design for the traffic signal alternative. The design decisions reflected in this exhibit include the following: • Appropriate length of the approach medians on US-21 to help make the intersection visible • Number of lanes and lane arrangement based on anticipated turning-movement volumes • Appropriate curve radii based on design vehicles • Appropriate taper lengths and deceleration lane lengths based on posted speed Exhibit 6-5. Traffic signal alternative for US-21/Sanderson Road.

68 Performance-Based Analysis of Geometric Design of Highways and Streets Similar to the roundabout alternative, the key reasons for considering these design elements in the alternatives development and evaluation stage is to determine their impact on performance (safety and operations), assess the feasibility of the traffic signal, and estimate potential right- of-way impacts of the alternative. While completed at a scaled sketch level, each intersection concept is completed at sufficient detail to allow a side-by-side comparison of the two forms. Primary Alternatives for Evaluation. The three primary long-term alternative solutions considered for the US-21/Sanderson Road intersection include the following: • A single-lane roundabout with wayfinding and gateway treatments • A traffic signal with wayfinding and gateway treatments • Current two-way stop-controlled intersection form with enhanced wayfinding and gateway treatments The overarching purpose of the wayfinding and gateway treatments is to help increase the intersection visibility for drivers on US-21, raise motorist awareness of the potential conflicts that may occur at the intersection, and direct visitors to use the US-21/Sanderson Road inter- section as the entrance to the tribal land. Many of the wayfinding and gateway treatments were based on principles in NCHRP Report 613: Guidelines for the Selection of Speed Reduction Treat- ments at High-Speed Intersections (4) and FHWA’s Low-Cost Safety Concepts for Two-Way Stop- Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3). 6.2.3 Evaluation and Selection 6.2.3.1 Estimated Performance and Financial Feasibility Authors’ Note: Sections 5.4 and 5.4.1 provide information and considerations regarding (1) how to estimate the performance of project alternatives or specific geometric design deci- sions and (2) how to assess the financial feasibility of those project alternatives or design decisions. Section 4.4 presents information regarding what resources are available within the profession to help conduct the performance analysis for each project alternative or geometric design decision. The primary intent of the intersection project for US-21/Sanderson Road is to reduce the frequency and severity of crashes. The secondary consideration is incorporating wayfinding and gateway treatments at the intersection. The performance evaluation and financial fea- sibility used to evaluate the primary alternatives focused on evaluating safety effectiveness as related to the likelihood of reducing crash frequency and severity. Estimating Performance. Exhibit 6-6 summarizes similar information as Exhibit 6-3 with the addition of tools or resources available to evaluate how those design elements and decisions relate to safety. Section 4.4 provides guidance on similar resources for safety, operations, access, and quality of service performance categories. Of the resources noted in Exhibit 6-6, the HSM (5) and FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Road- ways (3) were the primary resources used to quantify the anticipated crash reduction (severity and frequency) of the alternative solutions. NCHRP Report 613 (4) and FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3) also provided useful performance information regarding the potential for reduced speeds on the intersection approach. Incorporating Financial Feasibility. The project team incorporated a financial assessment into the alternatives evaluation to identify the relative cost effectiveness of each alternative. In

Project Examples 69 this project, the cost per mitigated crash was used as the performance measure to gauge the relative economic performance for an alternative. The evaluation did not quantify the potential benefits of reduced vehicle speeds, the wayfinding, or the gateway treatments because it is not currently possible to relate those attributes directly to anticipated reduction in crash frequency. In the ultimate improvement selection step, those attributes are considered qualitatively. Exhibit 6-7 summarizes the expected safety performance and cost effectiveness of the alterna- tives for the US-21/Sanderson Road intersection. The project team estimated the safety perfor- mance expected to result from each alternative using the resources summarized in Exhibit 6-6. In this instance, planning-level cost estimates were developed to assess the relative cost effec- tiveness of each solution and to inform prioritizing implementation of the project elements. The functional design sketches helped identify that the signalized intersection approach con- figuration would require modifying an existing bridge west of the intersection. This bridge con- struction greatly increased the cost of the signalized alternative compared to the roundabout concept. Benefit-cost ratios could also be used to assess the economic validity of alternative solutions; this would provide a sense of whether the potential benefits of a project are sufficient to justify its cost. The sole purpose of the financial assessment is to inform decisions of how best to allocate limited resources for greatest possible benefit. Performance Target Related Design Elements Related Design Considerations Tools or Resources to Evaluate Performance Reduce Total Number of Crashes; Reduce Severity of Crashes Intersection Control • Two-Way Stop All-Way Stop • Traffic Signal • Roundabout • Highway Safety Manual, Chapters 10 and 14 (5 ) • Supporting Software Tools: HiSafe; IHSDM Intersection Design Features • Left-Turn Lanes • Right-Turn Lanes • Presence of Lighting • Visibility of Intersections • Highway Safety Manual, Chapters 10 and 14 (5 ) • Supporting Software Tools: HiSafe; IHSDM • FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3 ) • NCHRP Report 613 (4 ) Increase Intersection Awareness/Visibility Cross-Sectional Elements • Lane Width • Rumble Strips • Median (painted or splitter island type) • FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3 ) • NCHRP Report 613 (4 ) Decrease Vehicle Speed on Intersection Approach Cross-Sectional Elements on Intersection Approach • Lane Width • Rumble Strips • Median (painted or splitter island type) • FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3 ) • NCHRP Report 613 (4) Alignment on Intersection Approach • Roadway Curvature • Sight Distance • Advance Signing • FHWA’s Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways (3) • NCHRP Report 613 (4 ) • Exhibit 6-6. Design elements related to crash frequency and/or severity.

70 Performance-Based Analysis of Geometric Design of Highways and Streets 6.2.3.2 Selected Alternative Authors’ Note: Section 5.4.2 presents considerations with respect to selecting a preferred proj- ect alternative or determining the appropriate specific geometric design decisions (e.g., radius of a horizontal curve). This information helped inform the following discussion and decision. Based on the alternatives evaluation, the tribe and DOT decided to implement a round- about at the US-21/Sanderson Road intersection. The roundabout, in combination with the wayfinding and gateway treatments, provides the greatest long-term potential for reducing the intersection crash frequency and severity. The roundabout also creates multiple opportunities for gateway treatments at and on approach to the intersection. Finally, the roundabout at the intersection proper and the splitter islands on the inter- section approaches create definitive visual cues and changes in roadway geometry to cap- ture motorists’ attention and aid in reducing approach speeds. Authors’ Note: Constructing a single-lane roundabout at the US-21/Sanderson Road inter section is quantitatively the third most cost-effective solution intersection with regard to reducing crashes. The tribe and DOT selected it over the two lower-cost configurations because the roundabout pro- vides the long-term safety benefits and creates the ability for the tribe to achieve some of its broader overarching goals of improving wayfinding to access the tribal village and casino as well as creating a gateway treatment to tribal land. This combination of considerations led to selecting the roundabout. 6.3 Project Example 2: Richter Pass Road Authors’ Note: Project Example 2 considers alternative alignments to improve safety and maintain mobility along a rural two-lane roadway. In this project example, we consider the tradeoffs related to the safety and mobility performance categories. Specifically, the project example demonstrates the tradeoffs between improving safety and maintaining a reasonable level of mobility, while minimizing project costs. The performance measure used for mobility incorporates the concept of inferred speed from FHWA’s Speed Concepts: Informational Guide (6). Speed Concepts outlines a performance- based perspective on the relationship between operating speed, posted speed, design speed, and inferred speed. The learning objectives of this project example include the following: • Illustrate the tradeoffs to consider when trying to achieve performance characteristics that may be counter to one another Location—Solution Expected Crashes/Year (No.) Estimated Reduction (%) Crashes Mitigated/ Year (No.) Design Life (Years) Planning- Level Cost Estimate Cost/Crash Mitigated Over Design Life Sanderson Road TWSC Intersection— FHWA Lane Narrowing 2.2 31 0.7 5 $45,000 $13,196 Sanderson Road TWSC Intersection— FHWA Splitter Island 2.2 68 1.5 5 $112,500 $15,040 Sanderson Road— Single-Lane Roundabout 2.2 71 1.6 20 $3.15 million $100,832 Sanderson Road— Traffic Signal 2.2 36 0.8 20 $5.61 million $354,167 TWSC: Two-way stop-controlled Exhibit 6-7. Initial design decisions/potential solutions and estimated performance.

Project Examples 71 • Use Speed Concepts and the concept of inferred speed in informing design decisions • Illustrate the design flexibility agencies have to not select the alternative with the lowest predicted number of crashes 6.3.1 Project Initiation 6.3.1.1 Project Context Authors’ Note: Using the considerations noted in Section 5.2.1, we are able to identify key characteristics of the project context likely to help inform the intended project outcomes, per- formance category, and performance measures we will use to develop and evaluate potential solutions. The following summary of the project context sets the foundation for the remaining activities within the performance-based analysis framework. In this project example, the topo- graphic constraints and their influence on roadway geometry is a key influencing factor in the solution development, evaluation, and selected alternative. Richter Pass Road is a two-lane rural roadway. Development has expanded from adja- cent urban areas and begun to impact the hillside that Richter Pass Road traverses. Over the last several years, there has been a gradual increase in residential homes and other develop- ment adjacent to and accessing the roadway. Richter Pass Road traverses the top of a hill and ridge with sections also built into the side of steeper portions of the hill and ridgeline. As a result, the roadway has limited to no shoulders along its curvilinear alignment constrained by the topography. The roadway commonly has steep sideslopes with drop-offs on one side of the roadway and retaining walls or cuts through rock on the other side of the roadway. Exhibit 6-8 provides a schematic of the study area. Exhibit 6-8. Project area schematic.

72 Performance-Based Analysis of Geometric Design of Highways and Streets With the steady increase in traffic volume along the roadway, there has also been an increase in crashes. The majority of crashes, approximately 72% within the last 3 years, were run-off-the- road crashes. In the past, the county and state DOT implemented a series of low-cost safety treat- ments including increased curve delineation, guardrail, and speed feedback signs. Exhibits 6-9 and 6-10 illustrate some of these treatments. The designated facility design speed is 55 mph. The posted speed is 45 mph. Advisory speed signs for horizontal curves along the roadway are as low as 15 mph in some locations. 6.3.1.2 Intended Project Outcomes Authors’ Note: The following summarizes the key information related to whom the project is intended to serve, what the project is intended to achieve (i.e., intended project outcome), the appli- cable project performance category (or categories), and the applicable performance measures. Section 3.1 provides guidance and anecdotal examples of how to identify whom the project is intended to serve and what the project is intended to achieve. Sections 3.2 and 3.3 describe the over- arching relationship and differences between defining project performance and geometric design per- formance. In this project example, similar to Project Example 1, the two are relatively closely aligned. The basic purpose is to improve safety while maintaining a reasonable level of mobility. We also used Section 5.2.2 to inform the following summary of the intended project outcomes. Sec- tion 5.2.2 provides specific considerations for identifying the intended project outcomes, corresponding Exhibit 6-9. Speed feedback sign improvement. Exhibit 6-10. Curve delineation improvements.

Project Examples 73 performance categories, and supporting performance measures. In this project example, safety and mobility are the performance categories of interest. We used Sections 4.4.2 (Mobility) and 4.4.5 (Safety) to select the performance measures: inferred speed and crash frequency. Residents along Richter Pass Road want to reduce crashes and crash severity. The county and DOT have jurisdiction over adjacent segments of the roadway. Both agencies are interested in making the corridor more consistent in its design to better meet driver expectations. The road- way alignment currently has horizontal curves designed for speeds of 15 mph to 50 mph. There is limited budget for treatments; however, the county and DOT recognize to achieve long-term increases in safety performance (i.e., decreases in the number and severity of crashes) invest- ments are needed beyond the previous low-cost improvements. The primary target audience for the project is the motorists traveling the roadway. This population comprises primarily residents in the area, commuting traffic, and some recreational traffic to access multiuse trails that traverse the hillside. The primary performance categories of interest are safety and mobility. The project is intended to improve safety while maintaining a reasonable level of mobility for motorists. The primary performance measures related to safety are the number and severity of crashes. The performance measure for mobility is travel speed, with the intent of establishing a reasonable travel speed for the corridor. To evaluate mobility, the project team selected inferred speed relative to the posted speed as the performance measure. Inferred speed is explained in greater detail within FHWA’s Speed Concepts: Informational Guide (6). The practical definition of inferred speed is the speed a motorist is able to drive without physically departing the travel lane; it is the speed as defined by the roadway geometrics. 6.3.2 Concept Development 6.3.2.1 Geometric Influences Authors’ Note: We used the information presented in Section 5.3 and specifically Section 5.3.1 for guidance on how to approach identifying the geometric influences for the project. We used Section 4.4 to help inform, at a more detailed level, the specific geometric characteristics likely related to the key project performance measures. The horizontal roadway alignment and potential for increased shoulder width were selected as the primary geometric elements on which to focus in developing alternative solutions for Richter Pass Road. These elements were selected as the focus because of the proportion of run-off-the-road crashes. Horizontal curvature (i.e., curve radii, super- elevation, and length) has been found to have a definitive, quantifiable impact on crashes occurring on rural two-lane roadways. The same basic horizontal alignment elements also have a direct impact on inferred speed, which is the selected metric for mobility. Similarly, shoulder width, and to a lesser degree shoulder type, have also been found to definitively influence crash occurrence on rural two-lane roadways. Under the given project context, the combination of horizontal alignment and shoulder width are likely to have the largest impact on the intended project outcomes of improving safety and establishing reasonable mobility for the roadway. Additional guidance for identifying the design elements that influence or are influenced by a given performance measure can be found in Section 4.4. 6.3.2.2 Potential Solutions Authors’ Note: Section 5.3.2 provides useful information and considerations for how to develop potential solutions given the specific project context, intended outcomes, performance measures, and influential geometric elements.

74 Performance-Based Analysis of Geometric Design of Highways and Streets The critical balancing act in developing potential solutions for Richter Pass Road, and ulti- mately selecting the preferred solution, will be the project costs. The terrain and topography through which Richter Pass Road passes likely necessitates cut, fill, and retaining walls for nearly any change in horizontal alignment or shoulder width. As a result, designs with greater require- ments for cut, fill, and/or retaining walls are likely to be considerably more expensive than other alternatives. Considering the project context, intended outcomes, and geometric elements most likely to influence the key project performance measures, the project team explored alternatives that reflect a range of investment and construction magnitude within which design solutions may be considered and evaluated These alternatives consist of four basic types:. • Basic Alternative 1—Minimal Improvements: Maintain current alignment and increase shoulder width. This represents the minimal investment the County and DOT are expecting to make in improvements. • Basic Alternative 2—Ultimate Improvements: Modify alignment to meet AASHTO criteria for 55 mph design speed and increase shoulder width. This represents a more traditional “ultimate” roadway build-out in which Richter Pass Road would be reconstructed to be con- sistent with design criteria that matched its current functional designation (e.g., design speed of 55 mph). • Basic Alternative 3—Practical Improvements: Modify alignment for consistent inferred speed and change posted speed to match inferred speed; this may result in a lower posted speed than exists. This represents a moderate design that is intended to strike a balance between Alternatives 1 and 2 and provide a long-term alternative solution. In this instance, Alternative 3 may help the county and DOT redefine and re-establish Richter Pass Road’s overarching purpose and function in the roadway network (i.e., does it really need to be a roadway that motorists can travel on at 55 mph?). • Basic Alternative 4—Subultimate Improvements: Modify alignment to meet AASHTO cri- teria for 55 mph design speed without increasing shoulder width. This represents a more traditional “interim” or “subultimate” improvement in which Richter Pass Road would be reconstructed to match its currently designated design speed and additional investment needed for increasing the shoulder width would be put off to a future date. The following subsections describe the resources used to develop the alternative solutions and considerations in further refining the basic alternatives into specific alternatives for evaluation. Resources Used to Develop Solutions. The project team used A Policy on Geometric Design of Highways and Streets (1), the DOT’s roadway design manual, and Speed Concepts (6) as the primary resources to develop and define the four alternatives. Solution Development. The key differentiating elements for the alternatives are horizontal alignment and shoulder width. The horizontal alignment elements for Alternatives 2 and 4 are already defined since a design speed of 55 mph is specified for those alternatives. A specific shoul- der width needs to be defined for Alternatives 1 and 2. A specific inferred speed needs to be estab- lished for Alternative 3 so the horizontal alignment elements can be designed. The project team does not have the scope, budget, or time to evaluate a full range of potential shoulder widths or a full range of potential inferred design speeds. Therefore, the project team narrowed the possible shoulder widths and inferred speeds to explore, based on the project context, intended project outcomes, and a fundamental understanding of how shoulder width and horizontal alignment influence safety and inferred speed. Preliminary Shoulder-Width Considerations. The existing Richter Pass Road has no measure able shoulder width; therefore, any increase in shoulder width is likely to provide a safety The critical balancing act in developing potential solutions for Richter Pass Road, and ultimately selecting the preferred solution, will be the project costs.

Project Examples 75 benefit. If an investment is made to add shoulder width, the county and DOT would like to see sufficient shoulder width to enable a disabled vehicle to pull to the side and leave a total of 22 ft available for other motorists to pass and incident response activities. The current lane widths are 12 ft, providing 4-ft shoulders in each direction would provide the residual 22 ft if a disabled vehicle pulled to the side of the roadway. This provides 10 ft of width for the disabled vehicle. The project team did a preliminary analysis of the potential crash reduction [using Chapter 10 of the HSM (5)] and cost per linear foot of increasing shoulder width from 0 to 2 ft and 0 to 4 ft. The preliminary analysis indicated the following: • Shoulder width 0 to 2 ft – 9% crash reduction – $20 per linear foot of 2-ft-wide paved shoulder (approximately $211,200 for 1 mi of 2-ft- wide paved shoulder in both directions) • Shoulder width of 0 to 4 ft – 17% crash reduction – $60 per linear foot of 4-ft-wide paved shoulder (approximately $633,600 for 1 mi of 4-ft- wide paved shoulder in both directions) Based on the preliminary screening and analysis, the county and DOT decided to carry for- ward Alternatives 1 and 2 using a shoulder width of 4 ft. The 4 ft of shoulder would provide 22 ft for vehicles to pass the disabled vehicle and for incident management activities. While the cost of adding 4 ft of shoulder is notably greater than 2 ft, the county and DOT decided it could be worth the investment given the potential crash reduction and space for incident management. There are limited alternative routes providing access to the residences off of Richter Pass Road; therefore, keeping the roadway open maintains local mobility and access. Preliminary Inferred Speed Considerations. The county and DOT recognize Richter Pass Road is performing a different function and role in the overall roadway network than when it was originally constructed. Since it was built as a rural arterial, larger roadway facilities have been created that provide parallel and more efficient regional connections. As a result, Richter Pass Road functions more as a collector road providing mobility and access to residents living in adjacent developments. Given these changes to the surrounding context of Richter Pass Road, discussions with the County, DOT, and community arrived at the general consensus that the pre- ferred operating speed for the roadway is 35 mph. Therefore, the inferred speed used to develop Alternative 3 was 35 mph. Primary Alternatives for Evaluation. Based on the solution development [i.e., establishing dimensional values for the shoulder widths (4 ft) and selecting an inferred speed (35 mph)] and refinement of the initial broad alternatives, the project team identified the four specific alterna- tive solutions for evaluation: • Alternative 1—Minimal Improvements: Maintain current alignment and increase shoulder width from 0 to 4 ft. • Alternative 2—Ultimate Improvements: Modify alignment to meet AASHTO criteria for 55 mph design speed and increase shoulder width from 0 to 4 ft. • Alternative 3—Practical Improvements: Modify alignment for consistent inferred speed of 35 mph and change posted speed to 35 mph to match inferred speed. • Alternative 4—Subultimate Improvements: Modify alignment to meet AASHTO criteria for 55 mph design speed without increasing shoulder width. Once the alternatives were more clearly defined, the project team used aerial imagery, survey data, and CAD software to lay out the alternatives and estimate right-of-way impacts, cut and fill requirements, and potential need for retaining walls. This meant including the dimensional

76 Performance-Based Analysis of Geometric Design of Highways and Streets values of a shoulder width of 4 ft and the horizontal curve radius, length, and superelevation for 35 mph (for Alternative 3) and 55 mph (for Alternatives 2 and 4). The team documented the resulting curve radii, length, superelevation, and shoulder width for each alternative. These geometric characteristics will be key inputs for calculating safety and mobility performance and estimating the cost for each alternative. Exhibits 6-11 (Alternative 2) and 6-12 (Alternative 3) illustrate the difference between the horizontal curves within the alternatives. A relatively quick visual inspection of the two curves clearly illustrates key differences in horizontal curve characteristics and the tradeoffs between the two fundamentally different approaches. • Alternative 2 is the traditional approach to bring a roadway up to meet its established stan- dard based on functional classification. Fewer curves, larger curve radii, and longer curves Exhibit 6-11. Alternative 2 horizontal alignment.

Project Examples 77 are key characteristics of the horizontal alignment in Alternative 2. This corresponds to higher inferred speeds, lower predicted crashes, higher cut/fill volumes, and higher con- struction costs relative to Alternative 3. • Alternative 3 is more of a pragmatic approach to modify the roadway to fit its physical context and current function and to establish consistent expectations for road users. The Alternative 3 horizontal alignment has more curves with smaller curve radii and is shorter in length compared to Alternative 2. This corresponds to the lower cut/fill estimates, lower construction costs, lower inferred speeds, and higher predicted crashes relative to Alternative 2. As will be discussed further, the two alternatives have notably different performance char- acteristics, impacts, and costs. The following section summarizes and discusses the perfor- mance and financial feasibility evaluation of the alternatives. Exhibit 6-12. Alternative 3 horizontal alignment.

78 Performance-Based Analysis of Geometric Design of Highways and Streets 6.3.3 Evaluation and Selection 6.3.3.1 Estimated Performance and Financial Feasibility Authors’ Note: Sections 5.4 and 5.4.1 provide information and considerations regarding (1) how to estimate the performance of project alternatives or specific geometric design deci- sions and (2) how to assess the financial feasibility of those project alternatives or design decisions. Section 4.4 presents information regarding what resources are available within the profession to help conduct the performance analysis for each project alternative or geometric design decision. The performance evaluation focused on safety as defined by crash frequency and mobil- ity as defined by inferred speed (used as a surrogate for operating speed). Estimating Performance. Chapter 10 of HSM (5) was used to estimate the impact each alternative had on crash frequency. Speed Concepts (6) was used to evaluate each alternative’s impact on inferred speed relative to posted speed. As discussed previously, the primary geomet- ric features influencing these performance characteristics are horizontal curves (radii, super- elevation, length) and shoulder width. Exhibit 6-13 summarizes the evaluation results for each alternative, including the estimated cut or fill required. Based on the safety and mobility evaluation results, Alternative 2 is estimated to result in the lowest frequency of crashes; however, it has one of the higher ranges of inferred speed and the largest average requirement of cut and fill. Alternatives 3 and 4 are estimated to have the next lowest average crash frequencies. Alternative 3 has the most consistency with inferred speed and requires the second lowest amount of average cut and fill. The tradeoffs shown in the table illustrate some of the considerations in trying to achieve mul- tiple performance characteristics and produce a financially feasible solution. The transportation profession’s research regarding crash prediction for rural two-lane roadways indicates longer hor- izontal curves with larger radii tend to result in fewer roadway departure crashes. Such horizontal curves also enable motorists to drive at higher speeds. In mountainous or rolling terrain, this can result in more cut or fill and therefore higher project costs. Research indicates horizontal curves that are shorter in length and have smaller curve radii tend to result in more roadway departure crashes (5). Such horizontal curves also result in slower motorist speeds, which is desirable in this context for Richter Pass Road. In mountainous and rolling terrain, shorter horizontal curves with smaller radii tend to require less cut or fill and therefore tend to be lower in cost. To help further inform the county and DOT’s selection of an alternative, the project team estimated the cost for each alternative. Alternative Safety Performance (crashes/yeara) Mobility Performance (inferred speedb) Average Cut or Fill Required per Station (yd3) No Project 13 15 to 55 mph 0 1 – Minimal 11 15 to 55 mph 100 2 – Ultimate 4 60 to 80 mph 700 3 – Practical 7 35 to 40 mph 200 4 – Subultimate 6 60 to 80 mph 450 aExpected (average) annual total crashes per year. bInferred speed of horizontal curves within study area. Exhibit 6-13. Evaluation results of each alternative.

Project Examples 79 Incorporating Financial Feasibility. The project team developed cost estimates for each alternative. The cost estimates took into consideration key cost drivers such as cut, fill, retaining walls, and right-of-way acquisition. Exhibit 6-14 summarizes the cost estimates with the evalu- ation results shown previously. The project team decided not to estimate a benefit/cost ratio or calculate a cost-effectiveness factor for each alternative. The county, DOT, and project team believed that would over simplify some of the considerations that cannot be monetized or quantified for a cost-effectiveness assessment. For example, the value and benefit of establishing a consistent and predictable road- way alignment for motorists (i.e., low variability in inferred speed) is not something that can be directly captured by a benefit/cost ratio or cost-effectiveness evaluation. The county and DOT used the cost estimate information in combination with the performance results and under- standing of the project context to select the preferred alternative. 6.3.3.2 Selected Alternative Authors’ Note: Section 5.4.2 presents considerations with respect to selecting a preferred proj- ect alternative or determining the appropriate specific geometric design decisions (e.g., radius of a horizontal curve). This information helped inform the following discussion and decision. The county and DOT decided to implement Alternative 3. Alternative 3 achieves the desired crash reduction relative to existing conditions. It also creates a uniform driving expe- rience for motorists; the alignment is consistently designed for 35 mph. The county, DOT, and community collectively agreed Richter Pass Road’s purpose and function are more aligned with serving a local mobility and access function. They agreed 35 mph is a more rea- sonable posted speed for motorists, and creating an alignment that inherently reinforces the posted speed of 35 mph is appropriate for the corridor. The county, DOT, and community recognize a lower speed for the roadway may slightly degrade mobility. However, they are willing to accommodate lower mobility for a more affordable safety improvement. Authors’ Note: Upon further discussion regarding Alternative 3, the county and DOT chose to explore further refining Alternative 3 by including the 6-ft-wide shoulders. The subsequent safety and cost evaluation indicated the 6-ft-wide shoulders reduced crashes to approximately six crashes per year and raised the total project cost to approximately $3 million per mile. Based on the limited additional reduction in crashes (one additional crash reduced per year with an increase in cost of $1.5 million per mile) and corresponding relatively significant increase in cost, the county and DOT decided to move forward with their original selection of Alternative 3 with 4-ft-wide shoulders. The performance-based analysis to inform the solution development and project decisions within this project example enabled the county and DOT to identify a solution that balanced their safety Alternative Safety Performance (crashes/yeara) Mobility Performance (inferred speedb) Cost per Mile No Project 13 15 to 55 mph $0 1 – Minimal 11 15 to 55 mph $633,600 2 – Ultimate 4 60 to 80 mph $5.0 million 3 – Practical 7 35 to 40 mph $1.5 million 4 – Subultimate 6 60 to 80 mph $4.3 million aExpected (average) annual total crashes per year. bInferred speed of horizontal curves within study area. Exhibit 6-14. Cost estimates for evaluation results.

80 Performance-Based Analysis of Geometric Design of Highways and Streets and mobility performance goals at a financially feasible level of investment. The agencies were able to look beyond the traditional approach (i.e., Alternative 2) of fully building out a roadway to meet a pre-defined standard that, in this instance, no longer coincided with the function the roadway was playing or was going to play in the future. The performance-based analysis framework gave the agencies the tools they needed to identify the critical elements of project context, intended project out- comes, key performance categories and measures influencing geometric considerations, and methods for evaluating each alternative’s anticipated performance. 6.4 Project Example 3: Cascade Avenue Authors’ Note: Project Example 3 illustrates how performance-based analysis can be integrated into reconstructing an existing auto-oriented urban arterial to incorporate complete street attributes with a focus on alternative street cross sections. In this project example, the project is initiated and championed by local business owners (i.e., local business improvement district) who would like to see the corridor revitalized in terms of the local economy and broader community livability. The learning objectives of this project example include the following: • Incorporate performance measures and decisions related to accommodating multiple modes • Illustrate tradeoffs between modes considering measures beyond mobility • Capture considerations and tradeoffs within a constrained physical environment The broader project objectives (i.e., increase economic vitality and community livability) are con- nected to geometric design performance categories of quality of service for multiple modes, safety, access, reliability, and mobility. Section 3.1.2 discusses how the intended project outcomes correspond to the performance categories. Sections 3.2 and 3.3 were used to help differentiate between and link together the project performance and geometric design performance. Section 4.4 helped inform the selection of specific performance measures within each performance category. 6.4.1 Project Initiation 6.4.1.1 Project Context Authors’ Note: Using the considerations noted in Section 5.2.1, we are able to identify key characteristics of the project context that are likely to help inform the intended project outcomes and the performance category and performance measures we will use to develop and evaluate potential solutions. The following summary of the project context sets the foundation for the remaining activities within the performance-based analysis framework. An important factor in the context of this project example is that the motivation for the project is being driven by members of the local business community who would like to see the corridor revitalized from an economic standpoint and also from a long-term livability perspective for the surrounding community. The local business community lobbied city staff and decision makers to study and imple- ment design solutions to Cascade Avenue. The intended project outcome is to make it a more comfortable, safe, and attractive urban street for transit riders, pedestrians, and bicyclists. Cascade Avenue is an urban arterial providing a north-south connection between the downtown district and a university campus approximately 2 mi north of downtown. It is currently a four-lane undivided arterial with on-street parallel parking and intermittent transit stops. Under the existing condition, there are no bicycle lanes and sidewalks are curb-tight (i.e., no landscape buffer between the sidewalk and roadway). The AADT volume for Cascade Avenue is 22,000 vpd. It is a key arterial for three different fixed transit routes serving approximately 45% of the transit riders traveling within the city.

Project Examples 81 Despite the lack of bicycle facilities on Cascade Avenue, it is already a frequently used route by bicyclists traveling between downtown and the university campus as it is the most direct route between those two origins-destinations. The posted speed on Cascade Avenue is 35 mph. Local law enforcement has a difficult time enforcing the posted speed during off-peak periods when traffic is relatively low. The higher speeds in off-peak travel periods make Cascade Avenue less attractive to pedestrians an d bicyclists. The local business community would like Cascade Avenue to become a more well-rounded city street. They would like people in the surrounding communities to see and use it as a place to spend time, visit shops, linger at cafes and restaurants, as well as use it to travel within the city. The business community’s overarching motivation for the project is to revitalize Cascade Avenue and the surrounding area economically. They see improvements to Cascade Avenue from an urban design and transportation perspective as critical to their mission. The city agreed to study the street and identify and evaluate a range of potential configurations to better serve multiple modes and create a more complete urban street environment. This project example documents the preliminary design development and evaluation of alter- native street cross sections. The primary condition requested by local business owners was to keep the potential solutions on Cascade Avenue within the existing 82-ft-wide right-of-way. The business community is open to removing the existing on-street parking as a means to pro- vide more space for other modes or uses. They are also in the process of gaining support from a broad base of local business owners to form a local improvement district (LID) to help fund the project. 6.4.1.2 Intended Project Outcomes Authors’ Note: The following subsection summarizes the key information related to whom the project is intended to serve, what the project is intended to achieve (i.e., intended project outcome), the applicable project performance category (or categories), and the applicable performance measures. Section 3.1 provides guidance and anecdotal examples of how to identify whom the project is intended to serve and what the project is intended to achieve. Sections 3.2 and 3.3 describe the overarching relationship and differences between defining project performance and geometric design performance. In this project example, the project purpose is to enhance the multimodal characteris- tics of Cascade Avenue in support of the local business improvement district that would like to have more pedestrian activity along the corridor as a means for revitalizing the surrounding community. There are no direct geometric performance measures for evaluating how well a project alternative will revitalize or facilitate economic or community growth. However, there are indirect geometric per- formance measures contributing to characteristics that would support economic and/or community revitalization (e.g., quality of service for pedestrians, bicyclists, and transit riders). We used the information in Chapter 3 to help differentiate between the project performance and geometric performance. We also used Section 5.2.2 to inform the following summary of the intended project outcomes, including the applicable performance categories. In this project example, safety, mobility, quality of service, accessibility, and reliability are the geometric performance categories contributing to the broader goal of improving economic vitality along the corridor. We used Sec- tion 4.4.1 (Accessibility) through 4.4.5 (Safety) to select the performance measures. The local business community is the champion for the project. They are the catalyst for iden- tifying and implementing a project on Cascade Avenue with the purpose of revitalizing the street and surrounding areas from an economic and livability perspective. The primary target audience is the business community stakeholders who would like to see transit riders, pedestrians, and bicyclists better served by Cascade Avenue. As a result, transit riders, pedestrians, and bicyclists are key road users served by the project. Secondary target audiences include local residents The local business community would like Cascade Avenue to become a more well- rounded city street.

82 Performance-Based Analysis of Geometric Design of Highways and Streets and existing motorists. The project will need to balance the impacts on existing automobile and transit service. The key agency stakeholders are the city and local transit agency. The city has jurisdictional responsibility over Cascade Avenue. Therefore, it will be responsible for capital improvements, maintenance, and operations of the street. The local transit agency currently has three of its major fixed-route bus routes using Cascade Avenue to serve a large portion of its ridership. The intent of the study is to improve the road user experience, provide access for road users not previously served, while enhancing the economic vitality and activity of the street. The per- formance categories selected are quality of service, safety, accessibility, reliability, and mobil- ity. The performance measures to be used to evaluate alternative roadway cross sections are as follows: • Quality of service—MMLOS from HCM2010 • Safety—Crash frequency and number and management of conflict points • Accessibility—Type and presence of facilities and transit service characteristics • Mobility—Average travel time • Reliability—Consistency in travel time These performance measures do not directly measure economic vitality for an area or the potential for economic vitality. However, they are connected to geometric characteristics and reflect characteristics influencing different road users’ quality of experience. For example, a bet- ter MMLOS grade for the pedestrian mode corresponds to roadway geometric characteristics more likely to create an attractive environment in which pedestrians feel safe and comfortable. This helps achieve the business community’s goal of transforming Cascade Avenue into a city street where people want to shop, dine, and generally spend time. Similar parallels can be drawn for the other performance measures listed. 6.4.2 Concept Development 6.4.2.1 Geometric Influences Authors’ Note: We used the information presented in Section 5.3 and specifically Sec- tion 5.3.1 for guidance on how to approach identifying the geometric influences for the project. We used Section 4.4 to help inform, at a more detailed level, the specific geometric characteris- tics that are likely related to the key project performance measures. Roadway cross-sectional elements were selected as the primary geometric elements likely to influence the performance measures noted in Section 6.4.1.2. These cross-sectional ele- ments include the following: • Lane width • Number of automobile through lanes • Bicycle facility presence and type (e.g., bicycle lanes, buffered bicycle lanes) • Sidewalk width • Presence and width of landscaped buffer between sidewalk and travel lanes • Presence and type of on-street parking (e.g., parallel parking, angled parking) • Bus-only lanes • Central roadway median The potential solutions discussed in the following section explore different combinations of cross-section characteristics and create a range of alternatives reflecting the tradeoffs inherent in trying to serve different travel modes within a constrained right-of-way. Additional guidance for identifying the design elements that influence or are influenced by a given performance measure can be found in Section 4.4.

Project Examples 83 6.4.2.2 Potential Solutions Authors’ Note: Section 5.3.2 provides useful information and considerations for how to develop potential solutions given the specific project context, intended project outcomes, performance mea- sures, and influential geometric elements. The primary constraint and challenge in developing solutions for Cascade Avenue is serving the range of existing and desired road users within the existing right-of-way. Automobiles are cur- rently given the majority of space on Cascade Avenue; therefore, additional alternatives developed for Cascade Avenue are oriented toward one or more combinations of better serving transit riders, pedestrians, and bicyclists. The four basic alternatives (including the existing condition) are: • Basic Alternative 1—Existing cross section oriented toward serving automobiles • Basic Alternative 2—Transit-oriented cross section • Basic Alternative 3—Bicycle- and pedestrian-oriented cross section • Basic Alternative 4—Hybrid of transit, bicycle, and pedestrian features Alternative 1 will serve as a common baseline for comparison across alternatives; it is the existing roadway that prioritizes space for automobiles. Alternative 2 focuses on serving transit vehicles and riders. The roadway features within Alternative 2 include elements such as transit- only lanes. Alternative 3 is oriented toward bicycle and pedestrian modes and includes features such as buffered bicycle lanes. Alternative 4 is a hybrid of Alternatives 2 and 3. It strives to bal- ance the needs of transit riders, bicyclists, and pedestrians. The following sections discuss the resources used to develop the solutions, the process, and the primary alternatives evaluated. Resources Used to Develop Solutions. The project team used the Urban Streets Design Guide published by the National Association of City Transportation Officials (NACTO) (7) as a resource for developing alternative cross sections. The team also used NACTO’s Urban Bikeway Design Guide (8) and AASHTO’s Guide for the Development of Bicycle Facilities, Fourth Edi- tion (9), in identifying and developing alternatives. They used these guidance documents in combination with the city’s local design guides and standards. The resources were particularly helpful in providing visuals, examples, and alternative approaches for addressing the challenge of serving multiple travel modes. This project example focuses on documenting the development, analysis, and selection of a new, basic cross section for Cascade Avenue. There is valuable infor- mation in these reference materials regarding design and operational strategies for managing conflicts between modes at intersections and within the transition areas influencing how well an overall street corridor serves road users. Solution Development. Each alternative cross section has a modal emphasis in contrast to the existing auto-oriented cross section. The cross-section alternatives were developed to be reasonable representations of a type of alternative. This means some design details (such as curb type) will be determined in later stages of project development. A common element among the alternatives is the lack of on-street parking. The local business community expressed interest in increasing pedestrian activity on the street and therefore the desire to focus on solutions providing more space for that activity. This approach is consistent with the broader city’s goals and policies to focus on projects serving person-trips rather than auto-only trips. This translates to creating more space for modes other than autos. The primary concern related to eliminating on-street parking on Cascade Avenue was that vehicles would use on-street parking in adjacent residential areas. The city is addressing this concern as part of a broader city-wide parking management plan encompassing the Cascade Avenue area as well as the downtown district and the area surrounding the university. Other tradeoffs considered by the project team while developing and identifying the spe- cific characteristics within each cross section included allocating lanes for specific modes. For

84 Performance-Based Analysis of Geometric Design of Highways and Streets example, providing a transit-only lane has the ability to improve mobility and reliability for transit riders by reducing the average travel time along the corridor for transit riders. It also provides more predictable operating conditions for transit vehicles in peak traffic conditions. However, allocating space to transit vehicles negatively impacts mobility (and potentially reli- ability) for automobiles because they are reduced to one lane in each direction of travel instead of the existing two lanes. Similar tradeoffs were considered related to providing bicycle lanes and wider sidewalks for pedestrians. Another characteristic reflected in two of the alternatives is adding a central landscaped median that would transform Cascade Avenue to a divided facility. There are documented safety benefits for autos and pedestrians in having a median. A median also provides space to implement landscaping to help improve the aesthetics of the corridor. As will be seen in Alternative 3, the project team also considered changes that would provide addi- tional designated space for pedestrians and bicyclists and create a buffer between pedestrians and bicyclists and moving vehicles. The intent of these features is to decrease the likelihood of crashes and improve the overall experience of traveling and spending time on Cascade Avenue. Primary Alternatives for Evaluation. Using the resources and considerations previously described in brief, the project team arrived at the following alternatives for evaluation: • Alternative 1—Existing (Auto-Oriented): Four-lane undivided roadway with on-street par- allel parking on both sides of the street. Alternative 1 is shown in Exhibit 6-15. • Alternative 2—Transit Oriented: Four-lane divided roadway with transit-only lanes and increased sidewalk widths. Alternative 2 is shown in Exhibit 6-16. • Alternative 3—Bicycle and Pedestrian Oriented: Two-lane divided roadway with a buffered bicycle lane, landscaped buffer, wider sidewalks, and shared auto-transit lane. Alternative 3 is shown in Exhibit 6-17. Exhibit 6-15. Cross section of existing roadway. Exhibit 6-16. Transit-oriented roadway cross section.

Project Examples 85 • Alternative 4—Hybrid of Transit, Bicycle, and Pedestrian Alternatives: Four-lane undi- vided roadway with transit-only lanes, bicycle lanes, and a wider sidewalk. Alternative 4 is shown in Exhibit 6-18. The exhibits demonstrate that the alternatives have the following elements in common: • Fall within the existing 82 ft of right-of-way width and, therefore, does not require additional right-of-way • Require changing the existing curb locations and, therefore, revising stormwater management and drainage along the corridor • Reduce the capacity for automobiles from two lanes in each direction to one lane in each direction • Remove on-street parking (as discussed previously) • Increase sidewalk width for pedestrians The differentiating factors across the alternatives influencing their performance include the amount of space designated for bicyclists, presence of a central median, the presence of a physi- cal buffer for pedestrians and bicyclists from motor vehicles, and the type of space allocated for transit vehicles. Additional critical issues that are not directly captured in the exhibits but that will need to be considered prior to selecting an alternative for implementation include the following: • Logistics (e.g., allocating designated zones) of truck loading and unloading for the businesses along Cascade Avenue Exhibit 6-17. Bicycle- and pedestrian-oriented roadway cross section. Exhibit 6-18. Hybrid of transit, bicycle, and pedestrian alternatives.

86 Performance-Based Analysis of Geometric Design of Highways and Streets • Definition of transition areas on approach to intersections or major driveways where vehi- cle turning movements will occur; these conflict areas will need to be managed particularly within alternatives providing transit-only and/or bicycle lanes • Revisiting, confirmation, and possibly modification of intersection control, lane configura- tions, and/or signal timing (if a signal is present) to better align with the selected cross section For example, if Alternative 2, the transit-oriented cross section, is selected, the city may want to implement transit signal priority to help maintain consistent and reliable transit service along the corridor. These additional considerations are not addressed within this project exam- ple but were considered in the broader context of implementing the selected cross-sectional alternative. 6.4.3 Evaluation and Selection 6.4.3.1 Estimated Performance and Financial Feasibility Authors’ Note: Sections 5.4 and 5.4.1 provide information and considerations regarding (1) how to estimate the performance of project alternatives or specific geometric design decisions and (2) how to assess the financial feasibility of those project alternatives or design decisions. Section 3.3.2 presents information on the broader performance categories applicable to geomet- ric design performance. Section 4.4 presents information regarding what resources are available within the profession to help conduct the performance analysis for each project alternative or geometric design decision. The performance categories evaluated for this project focused on the following: • Safety as defined by crash frequency, crash severity, and conflict points • Mobility as defined by average travel time • Reliability as defined by variation in travel time • Accessibility as defined by type and facility presence and transit service characteristics • Quality of service as defined by MMLOS The following paragraphs discuss how the performance was estimated for each alternative, results of the performance evaluation, results of the financial feasibility, and effectiveness of each alternative. Estimating Performance. To the extent feasible, the project team estimated the perfor- mance of each alternative quantitatively. However, in some cases, due to the state of the research and practice, a qualitative assessment was necessary. Exhibit 6-19 summarizes the resources used to calculate the performance of each alternative. Alternative Safety Mobility Reliability Accessibility Quality of Service 1 – Existing Condition HSM, Chapter 12 HCM2010 HCM2010 Qualitative Assessment HCM2010 2 – Transit Oriented HSM, Chapter 12 Principles HCM2010 HCM2010 Qualitative Assessment HCM2010 3 – Bicycle and Pedestrian Oriented HSM, Chapter 12 Principles HCM2010 HCM2010 Qualitative Assessment HCM2010 4 – Hybrid of Transit, Bicycle, and Pedestrian HSM, Chapter 12 Principles HCM2010 HCM2010 Qualitative Assessment HCM2010 Resource references: HSM (5 ), HCM2010 (10). Exhibit 6-19. Summary of resources for performance evaluation.

Project Examples 87 The project team faced several challenges in being able to quantitatively assess each alterna- tive across the range of selected categories and associated performance measures. The primary challenge was the gap in existing research findings. For example, research is not able to reflect the quantitative performance of the innovative street cross sections being considered for Cas- cade Avenue. The following list provides a more detailed description of how each resource can be used to estimate the performance measures identified above, including the instances when a qualitative assessment was necessary because of the lack of available research. • Safety. AASHTO’s HSM has methodologies (5) and information within it to be able to esti- mate the predicted safety performance for roadway cross sections of urban/suburban arterials. The HSM addresses cross sections ranging from two-lane undivided to five lanes (a five-lane cross section has two lanes in each direction with a two-way center turn lane). Therefore, the HSM can be used to estimate the long-term annual safety performance of Cascade Avenue under existing conditions. However, the remaining alternatives include cross-sectional features that cannot be evalu- ated using the HSM or other known resource: – The transit lanes present in Alternatives 2 and 4 – The buffered bicycle lane present in Alternative 3 – The traditional bicycle lane in Alternative 4 Therefore, the relative safety performance of these alternatives was considered qualitatively based on their abilities to separate conflicting modes and provide additional and/or protected space for vulnerable users (i.e., pedestrians and bicyclists). • Mobility. The project team used a software program to implement HCM2010 methodologies (10) and estimate the average travel time from one end of Cascade Avenue to the other. The average travel time was estimated for the morning, midday, and evening weekday periods, as well as the Saturday midday peak period. The intent of including the multiple periods was to obtain a sense of the range of travel time during low-, mid-, and high-traffic volume periods. The analysis focused on average travel time for motorists and transit vehicles (and, therefore, transit riders). • Reliability. As discussed in Section 4.4.4, research is ongoing within the transportation pro- fession to develop performance measures and a means to strengthen the connection between reliability and geometric design decisions. In the context of urban arterials, measuring the varia- tion in travel time is the best means for estimating relative consistency for motorists and transit riders on Cascade Avenue. To estimate the potential variation in travel time, the project team simulated traffic operations along the corridor for different periods of the day to reflect different traffic volume demands and introduced different unanticipated events (e.g., partial or full lane closure due to a crash or truck loading/unloading) to estimate the relative consistency in travel time for each alternative. The analysis focused on the variation in travel time for auto and transit vehicles. As will be seen in the results discussed later, providing a transit-only lane can notably help improve reliability for transit vehicles and riders. Results only speak to the reliability of the transit routes while they are traveling on Cascade Avenue; events may occur prior to or after the routes depart Cascade Avenue that negatively impact their overall reliability. • Accessibility. The project team evaluated access qualitatively, giving it an assessment of low, moderate, or high depending on the presence of facilities for specific modes and the transit service characteristics reflected in each alternative. Within this project context, additional access to the corridor for pedestrians, bicyclists, and transit riders was considered a positive performance characteristic given the overarching goal of the project to increase economic vitality of the corridor through increased pedestrian activity or person-trips. • Quality of Service. MMLOS was calculated using the methodology presented in the HCM2010 (10). The methodology produces a letter grade A through F to indicate the quality of the travel

88 Performance-Based Analysis of Geometric Design of Highways and Streets experience from specific road users’ perspectives. Therefore, it is possible for the same alterna- tive to produce a LOS C for bicyclists and LOS B for pedestrians. In other words, the methodol- ogy reflects that one street cross section can result in different qualities of experience depending on whether a person is walking, biking, taking transit, or driving an automobile. It is a useful methodology, particularly in combination with the HSM, because MMLOS captures some of the benefits from project elements the HSM cannot, such as bicycle lanes. The results of the performance analysis are summarized in Exhibit 6-20. The results for the safety and access evaluations are categorized as low, moderate, or high. In the context of this project, high performance in those two categories is desirable. High safety performance means, in a qualitative assessment, there is a lower likelihood of crashes and/or severe crashes due to attributes such as separate designated space for vulnerable modes, physical separation of vulnerable modes from motor vehicles, and other similar attributes. Exhibit 6-20 demonstrates it can be a complicated exercise to evaluate and interpret results from the evaluation of several alternatives across multiple modes using a variety of performance measures. Key themes the project team identified from the performance evaluation results included the following: • Safety. Alternatives 2 and 3 are expected to have better safety performance compared to other alternatives. This is attributable to the presence of the central median. The median separates Alternative Safety Mobility: Average Travel Time (min) Reliability: Variation in Travel Time (min) Accessibility Quality of Service: MMLOS 1 – Existing Condition Pedestrian Low — — Low D Bicycle Low — — Low F Transit Low 4.43 3.68 to 5.26 Moderate D Auto Low 2.67 2.42 to 3.17 High A 2 – Transit Oriented Pedestrian High — — Moderate C Bicycle Moderate — — Moderate E Transit High 4.40 3.68 to 4.76 High B Auto High 3.43 3.35 to 3.60 Low C 3 – Bicycle and Pedestrian Oriented Pedestrian High — — High B Bicycle High — — High C Transit High 4.80 3.97 to 6.00 Moderate D Auto High 4.80 3.80 to 6.10 Low D 4 – Hybrid of Transit, Bicycle and Pedestrian Pedestrian Low — — Moderate C Bicycle Moderate — — Moderate D Transit Moderate 4.38 3.65 to 4.78 High B Auto Low 3.45 3.32 to 3.56 Low C aThe exhibit summarizes results for the Saturday midday peak period. Similar summaries were prepared for the weekday evening and morning periods. — indicates not applicable. Exhibit 6-20. Performance evaluation resultsa.

Project Examples 89 vehicles moving in the opposite direction and provides a pedestrian refuge for pedestrian crossings at intersections and mid-block. These alternatives also include separate facilities designated for auto, transit, and bicycles. Furthermore, Alternative 3 includes additional buff- ering for pedestrians and bicyclists from motorized traffic. As noted previously, if Alterna- tives 2 or 3 is selected (or if Alternative 4 is selected), the project team will need to spend time designing transition areas to transition from the street cross section to intersections where vehicle turn movements will need to occur. Within Alternative 3, the team will also need to consider and develop an approach for managing conflicts between transit vehicles and bicy- clists on approach to transit stops. This may include strategies such as moving the transit stop to a platform away from the sidewalk and having the bicycle lane pass between the platform and the sidewalk. Alternatives 1 and 4 have the lowest expected safety performance. This is attributed to the lack of a central median and, in the case of Alternative 1, the lack of separate facilities for bicyclists and transit vehicles. • Mobility. Alternative 1 is expected to have the highest mobility (lowest average travel time) for motorists on Cascade Avenue, which is attributed to the four-lane cross section. Alter- natives 2 and 4 are the next two alternatives with higher mobility for motorists and transit vehicles. Each of these alternatives includes a transit and auto lane in each direction and, therefore, has similar mobility results for those modes. The average travel time reflected in Alternatives 2 and 4 is closer to the posted speed limit on Cascade Avenue of 35 mph, which is desirable with respect to safety (i.e., provides more time for motorists to react to roadway conditions and is more likely to result in less severe crashes in the event one occurs) and creating a more comfortable environment for pedestrians and bicyclists. • Reliability. Alternatives 2 and 4 have the highest reliability (i.e., lowest variation in travel time) for transit riders and motorists. While these two alternatives do not have the highest mobility for motorists, they do create moderately more consistent travel times. Increased reliability is achieved primarily by the transit lanes included within the alternatives. Transit lanes prevent motorists from being stuck behind a transit vehicle loading and unloading passengers. The increased reliability is also attributable to removing the on-street parking present in Alternative 1. Alterna- tive 3 has the lowest reliability for transit riders and motorists. This is because transit vehicles and motorists are sharing a single travel lane in each direction; therefore, transit stops, truck loading and unloading maneuvers, and incidents (and incident management) directly affect the space both modes need for travel. This creates the greater variation in travel time. • Accessibility. Alternatives 2, 3, and 4 provide similar levels of access for pedestrians, transit riders, bicyclists, and motorists. Within Alternatives 2, 3, and 4, access (with respect to being able to travel on Cascade Avenue and gain access to the businesses along it) range from mod- erate to high for pedestrians, transit riders, and bicyclists because of the presence of facilities for those modes. Within those same alternatives, access for motorists is evaluated as low. This is primarily because on-street parking is not included in Alternatives 2, 3 or 4. • Quality of Service. Alternative 3 provides the highest quality of service for pedestrian and bicycle modes. The high quality of service for pedestrians is attributable to the wider side- walks, landscaping buffer, and additional separation from motor vehicles gained from the adjacent buffered bicycle lane. For bicyclists, the higher quality of service is attributable to eliminating on-street parking, providing a designated bicycle lane, and including wider width for the buffered bicycle lane. Alternatives 2 and 4 provide the best quality of service for transit riders, which is primarily attributed to the operational benefits of the transit lanes (e.g., better service characteristics). This is in combination with the pedestrian improvements included in those alternatives. Motorists’ quality of service is highest in Alternative 1 because of the higher mobility and relatively few times motorists would need to stop. Motorists are expected to experience moderate quality of service within Alternatives 2 and 4. This is likely attributed to separating automobiles and transit vehicles to help manage the number of times motorists would need to stop while traveling the corridor.

90 Performance-Based Analysis of Geometric Design of Highways and Streets Given these considerations purely based on performance evaluation results, the project team and broader stakeholders felt Alternatives 2 and 3 had performance characteristics best reflect- ing the attributes they desired for Cascade Avenue. The following section discusses the financial feasibility considerations. Incorporating Financial Feasibility. The project team developed cost estimates for each alternative. The cost estimates considered critical characteristics such as the costs of curb reloca- tions, modifications needed to stormwater drainage and management, new pavement markings, revisions to signing, modifications to transit stop locations and configurations, improved illumi- nation, and landscaping and other similar costs associated with the unique characteristics of each alternative. Exhibit 6-21 summarizes the cost estimates for the alternatives. The significant elements influencing cost included modifying the stormwater drainage, adding a median, landscaping, changing transit stop locations and configurations, and pavement reha- bilitation. Many of these attributes are present within Alternatives 2, 3, and 4 to varying degrees. Alternatives 2 and 3 are higher in cost than Alternative 4 because of the median and additional landscaping that they include. The project team did not estimate a benefit/cost ratio or calculate a cost-effectiveness factor for the alternatives. To be able to calculate a benefit/cost ratio or cost-effectiveness factor, sim- plifying assumptions would be needed and some performance metrics omitted due to the lack of research and inability to quantify them. As a result, the city and project stakeholders did not want to oversimplify or omit performance measures they felt to be critical in selecting an alternative for Cascade Avenue. The city used the project cost information in combination with the performance evaluation results and understanding of the project context to reach consensus with project stake- holders on a preferred alternative. 6.4.3.2 Selected Alternative Authors’ Note: Section 5.4.2 presents considerations with respect to selecting a preferred proj- ect alternative or determining the appropriate specific geometric design decisions (e.g., presence of a median). This information helped inform the following discussion and decision. The city and project stakeholders selected Alternative 2 as the preferred alternative. Alternative 2 provides improved safety, reliability, access, and quality of service for transit riders, pedestrians, and bicyclists. Within this alternative, the bicycle quality of service is the least improved relative to transit riders and pedestrians’ anticipated experience. Within Alternative 2, bicyclists will need to share the transit lane with transit vehicles. This is an improvement over existing conditions because of the lower number of transit vehicles relative to automobiles and the width of the transit vehicle lane. The city felt most comfortable with the performance of Alternative 2. This is primarily because of the improvement in safety across modes and the preservation of reasonable mobility and reliability for motorists and transit vehicles. Cascade Avenue is a critical corridor for transit service within the city. There are limited parallel alternative routes for motorists to use in place of Cascade Alternative Cost per Mile 1 – Existing Condition $0 2 – Transit Oriented $1.4 million 3 – Bicycle and Pedestrian Oriented $1.6 million 4 – Hybrid of Transit, Bicycle, and Pedestrian $1.0 million Exhibit 6-21. Cost estimates.

Project Examples 91 Avenue that are not through residential areas. For those reasons, it was of high importance to the city to maintain a reasonable degree of mobility and reliability for motorists and transit, while better serving other modes. The local business community that initiated the Cascade Avenue improvements preferred Alternative 3 and Alternative 2 as their secondary selection. Attributes from Alternative 3 that the city plans to integrate into Alternative 2 to address the business community’s interests include adding landscaping along the sidewalks by using tree wells or other landscaping areas spaced at regular intervals. Attributes and characteristics to better serve bicyclists included elements such as bicycle corrals for easy parking in front of businesses; wayfinding signs for bicyclists; and signs and pavement markings to communicate to bicyclists and transit riders that bicyclists are permitted and encouraged to use the transit lane for travel. 6.5 Project Example 4: SR-4 Authors’ Note: Project Example 4 considers alternative shoulder widths and sideslopes along a rural collector roadway to improve safety while minimizing impacts to the adjacent environmentally sensitive area. The learning objectives for this project example are as follows: • Illustrate how performance-based analysis can be incorporated into an environmental review process • Discuss and explore tradeoffs between desired project performance and environmental impact In this project example, SR-4 is being improved to serve as an alternate route for a parallel high- way undergoing reconstruction. The performance categories considered within the project example are safety, reliability, and quality of service. Section 4.4 helped inform the selection of the specific performance measures used to evaluate the alternative solutions. 6.5.1 Project Initiation 6.5.1.1 Project Context Authors’ Note: Using the considerations noted in Section 5.2.1, we are able to identify key characteristics of the project context likely to help inform the intended project outcomes, per- formance categories, and performance measures we will use to develop and evaluate potential solutions. The following summary of the project context sets the foundation for the remain- ing activities within the performance-based analysis framework. In this project example, the motivation for the project is to improve SR-4 as an alternate route while a parallel highway undergoes substantial reconstruction. SR-4 is an east-west, two-lane rural highway passing through a biologically diverse and sensitive wetland. It runs roughly parallel to US-9, which borders the wetland area to the north. The two routes connect an established metropolitan area to the east and a growing suburban community to the west. The suburban area is transitioning from an established rural community to suburban development as growth in the urban metropolitan area pushes farther out from the urban core. SR-4 is frequently used by recreational cyclists in addition to motorists looking for a more direct and/or scenic route than is provided by US-9. SR-4 historically has had AADT of 9,500 to 10,100 vpd over the last 5 years. The additional traffic from the increased development west of the wetlands has tended to use US-9. US-9 AADT has increased from 15,000 to 18,750 vpd with similar growth trends anticipated for the next 5 to 10 years as development continues. The state DOT forecasts AADT on US-9 to grow to 23,500 vpd within a 5-year horizon. This is expected to increase to nearly 30,000 vpd within a 10-year horizon. The DOT prefers to continue to emphasize US-9 as the primary route to the

92 Performance-Based Analysis of Geometric Design of Highways and Streets metropolitan area to help preserve and limit the impact to the wetlands surrounding SR-4. The agency does recognize SR-4 is a critical alternate route to US-9 that should be maintained so it is able to continue to safely and reliably serve motorists and cyclists. The DOT has planned projects for SR-4 and US-9 to proactively improve their performance. This project focuses on identifying changes to SR-4 to proactively improve safety, reliability, and quality of service (as it relates to bicycle traffic), while minimizing negative impacts to the wetlands through which it travels. The existing cross section for SR-4 is two lanes, undivided, with 2-ft shoulders. The sideslopes are a relatively steep 2H:1V. The current roadway prism has a relatively narrow and limited footprint within the wetlands. 6.5.1.2 Intended Project Outcomes Authors’ Note: The following summarizes the key information related to whom the project is intended to serve, what the project is intended to achieve (i.e., intended project outcome), the appli- cable project performance category (or categories), and the applicable performance measures. Section 3.1 provides guidance and anecdotal examples of how to identify whom the project is intended to serve and what the project is intended to achieve. Sections 3.2 and 3.3 describe the overarching relationship and differences between defining project performance and geometric design performance. In this project example, the project purpose is to improve the safety and reliability of SR-4, in preparation for higher traffic volumes and additional use while the parallel state facility (US-9) undergoes substantial reconstruction. The governing agency also expects a relatively high number of recreational bicyclists to use SR-4. Therefore, quality of service for bicyclists is also an obvious performance characteristic to consider. Generally, similar to Project Examples 1 and 2, the project performance and geometric performance are relatively closely aligned. We used Section 5.2.2 to inform the following summary of the intended project outcomes. This includes the applicable performance categories. In this project example, reliability and safety are the geometric performance categories of interest. We used Sections 4.4.4 (Reliability), 4.4.3 (Quality of Service), and 4.4.5 (Safety) to select the performance measures. The DOT has planned large capital projects to expand US-9 from its existing two- and four- lane undivided cross sections to a consistent four-lane divided highway. To save money on construction costs and expedite completion of the project, the DOT has decided to close US-9 to traffic during the reconstruction and divert traffic to SR-4. In preparation for the additional traf- fic demand on SR-4 during construction, the DOT is considering alternatives to improve SR-4’s expected safety performance (for motorists and cyclists) and reliability. The DOT also sees long- term value in such projects on SR-4 because its long-term plan for managing the overall impact to the environmentally sensitive area is to limit roadway connectivity to the single route through the wetlands (SR-4) and a roughly parallel route to the north (US-9). The DOT would like to identify and implement treatments to SR-4 without the project esca- lating to a level of significant impact and requiring an EIS. Recently, the DOT conducted an EA for SR-4 that considered a wide range of alternative design solutions. From the EA, the DOT learned improving SR-4 to meet its roadway standards would result in a significant impact to the wetlands. The DOT also identified, from preliminary design work associated with the EA, an acceptable roadway footprint. This footprint would allow the DOT to reconstruct the roadway without having a significant environmental impact. Therefore, it could complete the project without an EIS. The purpose of this project is to identify the most effective cross section for SR-4 to improve safety, reliability, and quality of service for cyclists within the physical footprint defined from the EA. The primary audience is the motorists (including truck drivers) who will be diverted to use SR-4 while US-9 undergoes reconstruction and the bicyclists who currently use and will

Project Examples 93 continue to use SR-4. The DOT is the primary agency stakeholder as it has jurisdiction over the roadway; the local FHWA environmental office is also a key governmental stakeholder within the project. Community members of the developing area west of the wetlands and a community group focused on protecting the wetland are key broader public stakeholders. Safety will be measured as the frequency and severity of crashes. Reliability will be measured by the variation in travel time and will also be considered in the context of incident management. Incident manage- ment is of particular concern to the DOT because SR-4 will be the only route regionally available for east-west travel while US-9 is undergoing reconstruction. Quality of service for bicyclists will be evaluated based on the amount of space available for bicyclists on SR-4. 6.5.2 Concept Development 6.5.2.1 Geometric Influences Authors’ Note: We used the information presented in Section 5.3 and specifically Sec- tion 5.3.1 for guidance on how to approach identifying the geometric influences for the project. We used Section 4.4 to help inform, at a more detailed level, the specific geometric characteris- tics that are likely related to the key project performance measures. The roadway shoulder width and sideslopes were selected as the primary geometric characteristics on which to focus in developing alternative cross sections for SR-4. These were selected because they are known to substantively influence safety performance with respect to the occurrence and severity of run-off-the-road crashes. Run-off-the-road crashes are among the most prevalent crash types on rural roadways. Shoulder width and sideslopes also have a direct impact on reliability with respect to providing space for incident management, snow management, and/or disabled vehicles. Finally, shoulder width also has a direct impact on the amount of space, and therefore quality of service, for bicyclists. Center- line rumble strips and shoulder rumble strips were also considered as potential treatments to augment different combinations of shoulder width and sideslopes, with the intent of further reducing the likelihood of run-off-the-road and lane departure crashes. Additional guidance for identifying the design elements that influence or are influenced by a given performance measure can be found in Section 4.4. 6.5.2.2 Potential Solutions Authors’ Note: Section 5.3.2 provides useful information and considerations for how to develop potential solutions given the specific project context, intended outcomes, performance measures, and influential geometric elements. A key challenge in developing potential solutions for SR-4 is balancing the impact of an alter- native and the performance measures. The EA conducted by the DOT determined that as long as the design changes to SR-4 increased the total width of the roadway footprint (including the sideslopes) to no greater than 110 ft, then there would be no significant impact to the surround- ing environmentally sensitive area. Therefore, each of the alternatives developed and evaluated have a total width of no greater than 110 ft. The DOT would like to determine the most effective alternative to proactively address performance categories of safety, reliability, and quality of service for bicyclists while minimizing the impact to the surrounding environment. Community project stakeholders would also like to see as little impact as possible to the wetlands. Based on these considerations, the project team developed three basic alternatives in addition to the no-build alternative: • Basic Alternative 1—No-Build Condition: Maintains the existing roadway cross section and corresponding roadway prism. This serves as a consistent basis for comparison for each

94 Performance-Based Analysis of Geometric Design of Highways and Streets alternative and enables the DOT to address the basic question of whether investing in any of the alternatives provides sufficient value relative to how the existing condition is expected to perform. • Basic Alternative 2—Wide Shoulders: Increases shoulder widths to standard width for road- way functional classification and maintains similar sideslopes to the existing condition. This alternative represents the approach of substantially widening the shoulders to provide space for vehicles to recover if they drift from the travel lane, disabled vehicles, and incident man- agement in the event of a crash. This alternative also provides sufficient space to accommo- date recreational cyclists and install shoulder rumble strips. The sideslopes are similar to the existing condition; they are non-recoverable and not traversable (steeper than 3H:1V). They are relatively steep to minimize the physical impact to the surrounding area. If motorists were to leave the paved shoulder, they could lose control of their vehicle and face a higher prob- ability of the vehicle rolling down the sideslope to the bottom of the embankment. As a result, the likelihood of higher severity crashes for motorists that depart the paved shoulder is greater for this alternative relative to Alternative 3 or 4. • Basic Alternative 3—Moderate Shoulders and Sideslopes: Increases shoulder width, but to less than standard width, and adjusts sideslopes to be non-recoverable and traversable (3H:1V to 4H:1V). This represents an approximate hybrid of widening shoulders and softening the sideslopes of the roadway. The increased shoulder width is sufficient to provide clear safety benefits and some additional space for incident management, disabled vehicles, and bicy- clists. However, the shoulder width is not as wide as Alternative 2. The shoulder is not able to accommodate bicycle traffic and shoulder rumble strips. The sideslopes are considered tra- versable although not recoverable. This means motorists who depart the roadway and begin down the sideslope will be able to continue down the sideslope to the bottom without having their vehicle roll. However, they will not be able to regain sufficient control to re-enter the roadway or stop prior to the bottom of the slope. • Basic Alternative 4—Narrow Shoulders and Gradual Sideslopes: Maintains narrow shoul- ders and adjusts sideslopes to be recoverable. This represents the approach of maintaining the existing shoulder widths and focusing adjustments on the sideslope. Under this alternative, the sideslopes are modified to be a recoverable (4H:1V or greater) slope. This means motorists who depart the shoulder may possibly regain control of their vehicle and either bring it fully back onto the shoulder or bring it to a stop before it reaches the bottom of the embankment. Roadway departure crashes within this alternative have a lower probability of resulting in severe injury or injury crashes relative to the other alternatives. However, the narrow shoul- ders make it more difficult to accommodate incident management, disabled vehicles, and bicyclists on SR-4. The previous alternatives were identified to explore the relative effectiveness of, and relation- ship between, shoulder width and sideslopes at addressing the performance measures. Each has a different level of impact to the roadway prism and, therefore, evaluating the full range enables a better understanding of what is likely to produce the desired performance with minimal nega- tive impacts. The following describes the resources used to develop the alternatives above into specific alternatives for evaluation. Resources Used to Develop Solutions. The project team used AASHTO’s A Policy on Geo- metric Design of Highways and Streets (1), the DOT’s roadway design manual, and AASHTO’s Roadside Design Guide (11) as the primary resources to develop and define Alternatives 2, 3, and 4. Solution Development. The project team worked from the basic alternatives and the resources noted above to identify the specific shoulder width dimensions and sideslope charac- teristics defining each of the alternatives.

Project Examples 95 The key considerations influencing the selection of specific shoulder widths was the standard shoulder width dimension for a rural two-lane highway within the state. Another consider- ation was the approximate incremental safety effectiveness of wider shoulders, as documented in AASHTO’s HSM (5). The DOT’s roadway design manual identified 8 ft as the standard shoulder width for rural two-lane highways. The HSM documents that, to date, the profession has not seen a definitive incremental safety improvement from shoulder widths greater than 8 ft. There- fore, 8 ft is used as the upper bound for the shoulder-width dimension. And within the alterna- tives, 4 ft is used as a moderate increase to evaluate the combination of a moderate improvement in shoulder width and sideslope. The selection of sideslope dimensions was based on the concepts of what is considered a recoverable, non-recoverable but traversable, and non-recoverable and non-traversable side- slope. These are described as follows: • Recoverable sideslopes have a slope of 4H:1V or greater. Recoverable sideslopes enable drivers to maintain control of their vehicle and either bring it to a stop or return to the paved roadway section. These sideslopes result in a relatively large roadway footprint. This is why the recoverable sideslope incorporated into the alternatives was paired with a narrow shoulder width in an effort to minimize the impact on the surrounding area. • Non-recoverable but traversable sideslopes are those in the range of 3H:1V to 4H:1V. These sideslopes allow motorists to maintain sufficient control to reach the bottom of the embank- ment without their vehicle rolling or flipping, which helps reduce the potential for severe crashes. Traversable sideslopes have smaller footprints than recoverable sideslopes, but not as small as relatively steep sideslopes. Therefore, the traversable sideslope was combined with the moderate increase in shoulder width to understand if there is a middle ground between increasing the shoulder width and modifying sideslopes to minimize the roadway footprint. • Non-recoverable and non-traversable sideslopes are those steeper than 3H:1V. The foot- prints for these roadways are relatively small, but the risk for a severe crash is relatively high if a vehicle leaves the roadway. Therefore, the non-recoverable, non-traversable sideslope was combined with the relatively wide shoulders to provide motorists with additional space to maneuver without departing the roadway. In total, the combination of shoulder width and sideslope dimensions was identified to pro- vide the greatest opportunity to improve expected performance relative to safety, reliability, and quality of service for bicyclists, while also minimizing the impacts to the surrounding area. Primary Alternatives for Evaluation. Based on the project context, the primary alternatives the project team identified for evaluation, using the resources previously noted, are as follows: • Alternative 1—Existing Conditions: Two-lane undivided cross section with 2-ft-wide shoul- ders in each direction and roadside sideslopes of 2H:1V. Exhibit 6-22 illustrates the basic cross section. • Alternative 2—Wide Shoulders: Two-lane undivided cross section with 8-ft-wide shoulders in each direction and roadside sideslopes of 2H:1V. Exhibit 6-23 illustrates the basic cross section. • Alternative 3—Moderate Shoulders and Sideslopes: Two-lane undivided cross section with 4-ft-wide shoulders in each direction and roadside sideslopes of 3H:1V. Exhibit 6-24 illus- trates the basic cross section. • Alternative 4—Narrow Shoulders and Gradual Sideslopes: Two-lane undivided cross sec- tion with 2-ft-wide shoulders in each direction and roadside sideslopes of 4H:1V. Exhibit 6-25 illustrates the basic cross section. The project team evaluated the relative performance of each alternative and calculated the environmental impacts for each. The environmental impacts were quantified based on the

96 Performance-Based Analysis of Geometric Design of Highways and Streets Exhibit 6-22. Cross section of existing roadway. Exhibit 6-23. Cross section of wide shoulders. Exhibit 6-24. Cross section of moderate shoulders and sideslopes. Exhibit 6-25. Cross section of narrow shoulders and gradual sideslopes.

Project Examples 97 physical size of the roadway prism footprint and the additional impervious area the alternative would add to account for the potentially negative impact of additional stormwater runoff into the adjacent wetlands. 6.5.3 Evaluation and Selection 6.5.3.1 Estimated Performance and Financial Feasibility Authors’ Note: Sections 5.4 and 5.4.1 provide information and considerations regarding (1) how to estimate the performance of project alternatives or specific geometric design decisions and (2) how to assess the financial feasibility of those project alternatives or design decisions. Section 3.3.2 presents information on the broader performance categories applicable to geomet- ric design performance. Section 4.4 presents information regarding what resources are available within the profession to help conduct the performance analysis for each project alternative or geometric design decision. The performance evaluation focused on the following performance categories and asso- ciated measures: • Safety as defined by crash frequency and severity • Reliability as defined by the variation in travel time • Quality of service as defined by the space available for bicyclists Estimating Performance. Chapter 10 of AASHTO’s HSM (5) was used to estimate the expected safety performance for the alternatives. Methodologies from the HCM2010 (10) and a software program implementing those methodologies were used to estimate the variation in travel time to determine the reliability of each alternative. More specifically, reliability was mea- sured by simulating peak and off-peak traffic volume conditions and randomly incorporating incidents resulting in partial or full lane closures to determine the impact of unforeseen events such as crashes along the corridor. A similar approach was applied and discussed in Project Example 3. Principles from the HCM2010’s MMLOS methodology (10) were the basis for using shoulder width as a surrogate measure for the quality of service for bicyclists. The HCM2010 MMLOS methodology (10) is only directly applicable to urban and suburban contexts; however, the project team identified some principles that also seemed transferable to this rural context. The primary principle related to quality of service for bicycles was the amount of space allocated for their use separate from motor vehicles. In addition to the previous performance metrics, the project team also calculated two met- rics to use as surrogates for gauging each alternative’s relative impact to the surrounding envi- ronment: (1) the cross-sectional area of each alternative and (2) the impervious area of each alternative. Both of these metrics were calculated relative to existing conditions. Exhibit 6-26 summarizes the evaluation results for the alternatives. As reflected in the performance evaluation results, there is no single, clear alternative con- sistently performing better across each performance measure while also resulting in the lowest impact to the surrounding area. The project team identified the following trends in the analysis results: • Alternative 4 results in the most improvement with respect to safety and is the only alternative to not increase the impervious surface area. It has the lowest reliability and quality of service for bicyclists. It also has the largest increase in roadway cross-sectional area. • Alternative 2 is expected to provide the most reliability and highest quality of service for bicyclists. It has a slightly higher estimated annual crash frequency than Alternative 4. It also has the largest increase in impervious area among the alternatives but the lowest increase in roadway cross section.

98 Performance-Based Analysis of Geometric Design of Highways and Streets • Alternative 3 performs consistently in between Alternatives 2 and 3 with moderate results across the performance measures. Based on the performance results and assessment of the impact to the adjacent environmen- tally sensitive area, the DOT is considering Alternative 4 because of its safety performance, recov- erable sideslopes to mitigate the probability of severe roadway departure crashes, and the no net gain in impervious area. The following section discusses the financial feasibility considerations. Incorporating Financial Feasibility. The project team developed cost estimates for each alternative. The cost estimates took into consideration costs associated with earthwork for adjusting the roadway sideslopes and new and rehabilitated pavement, and other similar costs. Exhibit 6-27 summarizes the cost estimates for the alternatives. The significant elements influencing cost included adding new pavement and needing to rehabilitate existing pavement. Earthwork for modifying the sideslopes was the other significant factor for cost. As a result, Alternative 2 was estimated to be the most expensive alternative given that it includes both fill to widen the roadway and additional pavement work. Alternative 3 was also on the higher side for similar reasons, and Alternative 4 was the least expensive due to the lack of pavement work. The project team did not estimate a benefit/cost ratio or calculate a cost-effectiveness factor for the alternatives. To be able to calculate either a benefit/cost ratio or cost-effectiveness fac- tor, simplifying assumptions would need to be made to associate monetary values with metrics such as quality of service for bicyclists, increase in roadway cross-sectional area, and increase Alternative Safety (crashes/ year)a Reliability (minutes)b Quality of Servicec Increase Relative to Alternative 1 Roadway Prism Cross-Sectional Area (ft2/ft) Impervious Surface Area (ft2/ft) 1 – Existing Conditions 6.0 16.5 to 11.0 Low 0 0 2 – Wide Shoulders 4.9 13.8 to 11.0 High 120 12 3 – Moderate Shoulders and Sideslopes 4.6 18.9 to 11.0 Moderate 140 4 4 – Narrow Shoulders and Gradual Sideslopes 4.3 20.6 to 11.0 Low 200 0 a The safety analysis applies the methodology from Chapter 10 of the HSM to calculate expected annual average crash frequency. Within that methodology, roadside sideslopes are captured within the roadside hazard rating crash modification factor. b Reliability was measured by simulating peak and off-peak traffic volume conditions and randomly incorporating incidents resulting in partial or full lane closures to determine the impact of unforeseen events such as crashes along the corridor. A similar approach was applied and discussed in Project Example 3. c Quality of service for bicyclists is noted as low, moderate, or high based on the shoulder width within the alternative (high indicates a more desirable quality of service for bicyclists). Exhibit 6-26. Summary performance evaluation results. Alternative Cost per Mile 1 – Existing Conditions $0 2 – Wide Shoulders $1.8 million 3 – Moderate Shoulders and Sideslopes $1.1 million 4 – Narrow Shoulders and Gradual Sideslope $900,000 Exhibit 6-27. Cost estimates for Project Example 4

Project Examples 99 in impervious surface area. As a result, the DOT and project stakeholders did not want to over- simplify or omit performance measures they felt to be critical in selecting an alternative for SR-4. The DOT used the project cost information in combination with the performance evaluation results and understanding of the project context to reach consensus with project stakeholders on a preferred alternative. 6.5.3.2 Selected Alternative Authors’ Note: Section 5.4.2 presents considerations with respect to selecting a preferred proj- ect alternative or determining the appropriate specific geometric design decisions (e.g., should width). This information helped inform the following discussion and decision. The DOT and project stakeholders selected Alternative 4 as the preferred alternative. Alternative 4 improves the expected safety performance the greatest and has the lowest impact with respect to an increase in the impervious area. It also stays within the footprint defined by the EA to avoid a significant environmental impact to the surrounding area. Given these performance attributes, the DOT felt it was the most cost-effective improve- ment for SR-4. It addressed the agency’s primary concern of proactively improving safety along SR-4 and helping to continue to preserve the surrounding wetlands. The lack of additional impervious surface for the roadway was particularly attractive to the DOT because it would help the DOT manage the potentially negative impacts that runoff from roadways can have to wetland water quality. When wetland water quality is compromised, it creates issues for the plants, animals, and insects that have habitats in the wetlands. Selecting an alternative with more potential to compromise wetland water quality would put the project at risk of having an elevated environmental document (EIS). Alternative 4 does not provide a particularly high level of reliability or quality of service for bicyclists. The DOT addressed these potential performance issues through two different pro- grams. To address reliability, the DOT developed an incident response and management pro- tocol and process. It made use of an existing team of response vehicles to help disabled vehicles and respond to crashes. The existing team was expanded and a specific subgroup was assigned to SR-4 during the period of time when US-9 was closed for reconstruction. The response team was also expanded to include local tow truck companies placed on a special on-call list to promptly respond to incidents. To address quality of service for bicyclists, the DOT chose to manage bicycle traffic by disseminating information about alternative cycling routes (i.e., alternatives to SR-4) that bicyclists could use for recreational purposes while US-9 was closed for reconstruc- tion and SR-4 was serving the re-routed motor vehicle traffic. 6.6 Project Example 5: 27th Avenue Authors’ Note: Project Example 5 considers alternative alignments and cross sections for a new urban collector roadway. A new urban collector, 27th Avenue, is being designed to provide additional connectivity within and access to an industrial area. The overarching intended project outcome is to entice and encourage new employers to the newly zoned industrial area. The city, within which the industrial area is located, would like to increase its industrial employment base. The new urban collector would connect to the broader roadway network by way of existing US-33. The learning objectives for this project example are as follows: • Illustrate how to consider the broader context before beginning the details of design • Demonstrate how the needs of different modes can be balanced • Apply the performance-based analysis process within an EA The performance categories considered within the project example are access, quality of service, and safety. Section 4.4 helped inform the selection of the specific performance measures used to

100 Performance-Based Analysis of Geometric Design of Highways and Streets evaluate the alternative solutions. This project example is first introduced within Sections 3.1.1 and 3.1.2 in the discussion regarding how to identify whom a project is serving and what is trying to be achieved. 6.6.1 Project Initiation 6.6.1.1 Project Context Authors’ Note: Using the considerations noted in Section 5.2.1, we are able to identify key characteristics of the project context likely to help inform the intended project outcomes, per- formance categories, and performance measures we will use to develop and evaluate potential solutions. The following summary of the project context sets the foundation for the remaining activities within the performance-based analysis framework. The key motivator for this project is to make improvements to the roadway network to encourage and draw additional employers to the industrial area adjacent to US-33. The city is trying to increase the number of industrial employment opportunities to cre- ate a more well-rounded local economy. The city council approved expanding the indus- trial zone adjacent to the existing heart of the city’s industrial land uses. To draw in larger industrial-type employers and supporting services, the city is going to construct some of the necessary street infrastructure to make the new area viable for employers. The area is bounded by a steep hillside to the west, the downtown core to the south, and existing industrial uses to the north and east. An existing highway, US-33, runs along the newly zoned area’s north- easterly border. Exhibit 6-28 illustrates the location of the expanded industrial zone. Despite the proximity to rail, other industrial uses, and US-33 (a regional highway), there are some inhibitors for industrial employers. There is not sufficient connectivity within the newly zoned area to facilitate its use without heavy reliance on US-33. US-33 has relatively stringent access spacing standards, making it difficult to obtain access permits from the state DOT. Also, there are limited access points to the area and those that do exist are not consistently conducive to heavy-vehicle traffic. US-33 serves the existing industrial uses in the area while being a critical connection between the downtown and a regional park located to the north. As a result, US-33 is heavily traveled by recreational bicyclists traveling between downtown and the regional park. This high demand occurs despite the lack of bicycle lanes on US-33 and the variation in the paved shoulder width from 2 to 4 ft along the corridor. 6.6.1.2 Intended Project Outcomes Authors’ Note: The following summarizes the key information related to whom the project is intended to serve, what the project is intended to achieve (i.e., intended project outcome), the appli- cable project performance category (or categories), and the applicable performance measures. Section 3.1 provides guidance and anecdotal examples of how to identify whom the project is intended to serve and what the project is intended to achieve. Sections 3.2 and 3.3 describe the overarching relationship and differences between defining project performance and geometric design performance. In this project example, the project purpose is to make improvements to the roadway network to encourage and entice employers to the existing industrial area. There are no direct geo- metric performance measures for evaluating how well a project alternative will encourage or entice employers to the industrial area. However, there are indirect geometric performance measures con- tributing to characteristics that would support encouraging employers within an industrial area (e.g., quality of service for large vehicles, access to regional highways or freeways). We used the information in Chapter 3 to help differentiate between the project performance and geometric performance. We also used Section 5.2.2 to inform the following summary of the intended project outcomes, including the applicable performance categories. In this project example,

Project Examples 101 accessibility, quality of service, and safety are the geometric performance categories of interest. We used Sections 4.4.1 (Accessibility), 4.4.3 (Quality of Service), and 4.4.5 (Safety) to select the perfor- mance measures. City planners would like to address some of the inhibitors for industrial employers, while also addressing some of the issues related to mixed bicycle and heavy-vehicle traffic on US-33 within an area that does not have sufficient space for both modes. The city has decided to focus their investment on improving connectivity within the newly zoned area. In doing so, it hopes to address some of the deterrents for employers and explore ways to improve bicycle accom- modations from the downtown area to the regional park. The city’s basic approach for achieving this goal is to plan, design, and construct a new urban collector, 27th Avenue, within the newly zoned industrial area. The city plans to seek federal funding for part of the 27th Avenue project. Enough work has been done to know the project does not qualify for a categorical exclusion, and so the city needs to perform an EA to determine if the project could result in significant environmental impacts. The project did not qualify for a categorical exclusion due to its proximity to the hillside (pre- viously shown in Exhibit 6-28), which is a federally listed critical habitat. Considering the new Exhibit 6-28. Existing conditions of new industrial area.

102 Performance-Based Analysis of Geometric Design of Highways and Streets 27th Avenue, the city will need to avoid, and demonstrate there is no, significant impact to the hillside from the 27th Avenue construction. If it is unable to demonstrate no significant impact, the city will need to produce an EIS. The city would prefer to avoid significant environmental impact and, therefore, plans to adapt the 27th Avenue project design accordingly. With respect to funding, a LID has also been formed to generate funds for ongoing main- tenance and improvements within the newly zoned industrial area. The city will operate and maintain the roadway when it is constructed. The primary audience to be served by this project is heavy-vehicle operators who will need to be able to easily access and circulate within the industrial area. The city knows this is a critical factor industrial businesses consider in selecting their location. The secondary audience or users who also need to be considered in developing 27th Avenue are bicyclists and motorists traveling between the regional park and downtown districts. The other participating stakeholders are the business owners in the area participating in the LID that will help with funding 27th Avenue. The overarching intended outcome of the project, from the city’s perspective, is to entice industrial employers to the newly zoned industrial area. The city wishes to generate employment opportunities for an employment group that is currently an under-employed segment of the city’s population. There are no clear direct performance measures connecting design decisions to generating additional industrial-based jobs within an area. There are surrogate transportation performance categories and associated measures reflecting the type of roadway system industrial- based businesses value. The project team identified those key performance categories as accessi- bility, quality of service, and safety. The performance measure to be used for access is the ease with which heavy vehicles will be able to navigate the industrial area and the quality of access to US-33 and the downtown. The performance measure selected to measure quality of service is MMLOS performance for bicyclists (to access the regional park) and transit riders (to serve employees accessing jobs within the industrial area). The expected frequency and severity of crashes will be used to measure safety. 6.6.2 Concept Development 6.6.2.1 Geometric Influences Authors’ Note: We used the information presented in Section 5.3 and specifically Sec- tion 5.3.1 for guidance on how to approach identifying the geometric influences for the project. We used Section 4.4 to help inform, at a more detailed level, the specific geometric characteris- tics likely related to the key project performance measures. The project team decided to focus the initial alternative development and analysis on two elements: (1) obtaining a finding of no significant environmental impact and (2) creat- ing design attributes and parameters supporting the transportation performance measures previously identified. Roadway alignment is the primary factor influencing whether the 27th Avenue project can avoid a significant environmental impact. The critical habitat is part of the hillside and at the base of the hillside along the western border of the newly industrially zoned area. Therefore, horizontal alignment of 27th Avenue was one area of focus and consideration with respect to geometric design decisions. In addition to the roadway alignment, the project team also elected to focus on defining a set of cross-section design parameters that can be used to develop 27th Avenue. The cross sections must balance some of the performance tradeoffs between access for heavy vehicles, quality of service for bicyclists and transit riders, and safety across modes. The project team selected the

Project Examples 103 following design parameters to explore because of their direct relationship to the previously mentioned performance measures: • Intersection geometry as it relates to being able to accommodate large vehicles (e.g., radius of curb returns) • Lane width • Bicycle facility presence and type (e.g., bicycle lanes) • Ability to accommodate transit • Sidewalk presence and width for pedestrians and transit riders See Section 4.4 for additional guidance for identifying the design elements that influence or are influenced by a given performance measure. 6.6.2.2 Potential Solutions Authors’ Note: Section 5.3.2 provides useful information and considerations for how to develop potential solutions given the specific project context, intended outcomes, performance measures, and influential geometric elements. The project team’s initial effort focused on defining the alignment for 27th Avenue. Three alignment options were developed and assessed based on their ability to avoid a significant envi- ronmental impact, provide access to US-33 and downtown, and facilitate circulation within the industrial zoned area. In addition, the alignments ideally should not preclude reasonably sized parcels for large and smaller supporting employers. A brief description of each of the alignment options follows: • Alignment 1—US-33 and Interstate Access: Provides connection to US-33 and to I-7. Divides the newly zoned area into four quadrants. • Alignment 2—Rail Yard and Port Access: Provides a direct connection to US-33, rail yard and port. Divides the newly zoned area into two large parcels. • Alignment 3—US-33, Interstate, and Downtown Access: Provides a connection to US-33, I-7, and three minor arterials in the northern downtown core. Maintains the most contiguous amount of industrial land. Exhibit 6-29 illustrates the alignment options. Each of the alignment options can be paired with a set of design parameters helping to define the 27th Avenue cross section. The project team developed three sets of alternative design parameters considering the differ- ent road users to be served by 27th Avenue: • Alternative 1—Freight Oriented: A set of design parameters focused on characteristics facili- tating the movement of large vehicles. • Alternative 2—Freight with Bicycle Accommodations: A set of design parameters incorpo- rating characteristics for large vehicles and bicyclists. • Alternative 3—Complete Street: A set of design parameters considering characteristics of large vehicles, bicyclists, and transit riders. The following subsections discuss the resources used to develop the potential solutions, con- siderations in developing the solutions, and the more refined alternatives the project team evaluated for 27th Avenue. Resources Used to Develop Solutions. The project team used AASHTO’s A Policy on Geo- metric Design of Highways and Streets (1), the city’s roadway design standards, the state’s high- way design manual, and NACTO’s Urban Streets Design Guide (7) as references and guidance materials to develop specific alternatives for evaluation.

104 Performance-Based Analysis of Geometric Design of Highways and Streets Solution Development. In this project, the project team was challenged to consider a range of options for an alignment as well as cross-section characteristics to try to achieve the varied performance measures previously discussed. To keep the solution development within a rea- sonable scope of effort, the project team focused the alignment options on avoiding significant environmental impacts, providing access to the broader transportation network, and enabling onsite circulation. The options identified for the roadway cross-section design parameters are focused on elements that provide sufficient space for heavy vehicles (as a form of accessibil- ity), quality of service for bicyclists and transit riders, and safety. In developing the alignment options, some consideration also was given to how to augment the options to better serve (1) bicyclists currently using US-33 to access the regional park and (2) safety with respect to speed management. Alignment Options for 27th Avenue. Alignment options for 27th Avenue were developed considering the connections to regional transportation facilities and the need to avoid a sig- Exhibit 6-29. Alignment options for 27th Avenue.

Project Examples 105 nificant environmental impact. The potential connections to regional transportation facilities include the following: • US-33—A highway serving as a key transportation freight corridor reaching from coastal communities west of the industrial area to urban, suburban, and rural mountain communi- ties east of the industrial area. • I-7—An Interstate freeway passing north-south through the state, connecting the majority of the major coastal cities and ports. • Rail Yard—The rail yard is served by two major freight rail lines traversing east-west across the state, ultimately connecting to a major interstate rail hub. • Port (River)—Provides access to large merchant and freight-carrying ships with access to the ocean and, therefore, access to a wide range of global ports. • Downtown—Connection to areas where employees will be traveling to and from their places of residence. It is also a connection to existing transit service and bicycle boulevards. The project team explored different options and degrees of direct connections to these regional transportation facilities. There are advantages and disadvantages to directly connecting to any one of these regional facilities. The direct access can be attractive to industrial employers; however, depending on the existing operations of that facility, it may result in operational delays or limited capacities by adding industrial traffic directly to an already well-used facility. Directly connecting to the downtown also presents potential considerations with respect to cut-through traffic and the general advantages and disadvantages of expanding the downtown street grid. One key advantage the city wanted to capture in one of the options was the ability to provide an alternate route and better quality route for bicyclists traveling to the regional park so bicyclists would not be forced to use US-33. Design Parameters for 27th Avenue Cross Section. Design parameters for the 27th Avenue cross section were identified based on the road users that 27th Avenue is intended to serve. Any of the alternative cross sections can be paired with any one of the alignment options previously discussed. A common element between the cross sections is the consideration given to accommodat- ing large vehicles needing to routinely access the industrial uses. As additional road user design elements are incorporated into the cross section, the project team tried to balance the ultimate roadway width with providing sufficient space for different road users. This was an ongoing tradeoff in developing and evaluating the different cross sections. The city would like to keep the total cross-section width as narrow as possible while still meeting road users’ needs. A nar- rower cross-section footprint will allow more space for the industrial uses and employers that the city would like to attract to the area. The clear tradeoff in keeping the roadway cross-section footprint narrow is having less space to serve the large vehicles, bicyclists, and transit riders who are anticipated to use 27th Avenue. The city made one overarching design decision applied to each alternative cross section. The city decided 27th Avenue will be an undivided roadway facil- ity; therefore, none of the alternatives include a center median. The primary reason for this is to keep the roadway cross section open and free of physical obstacles, providing more space and options for drivers of heavy vehicles to navigate the industrial area. Primary Alternatives for Evaluation. Using the resources and considerations briefly described previously, the project team arrived at the alignment options shown in Exhibit 6-29 and the following alternative cross sections for evaluation: • Alternative 1—Freight-Oriented: Two-lane roadway with 14-ft-wide travel lanes and a 16-ft- wide, two-way center left-turn lane (total three-lane cross section). Cross section includes curb-tight 5-ft-wide sidewalks on both sides of the street. Shown in Exhibit 6-30.

106 Performance-Based Analysis of Geometric Design of Highways and Streets • Alternative 2—Freight with Bicycle Accommodations: Two-lane roadway with 12-ft-wide travel lanes and a 14-ft-wide two-way center left-turn lane (total three-lane cross section). Cross section includes 6-ft-wide bicycle lanes and curb-tight 5-ft-wide sidewalks on both sides of the street. Shown in Exhibit 6-31. • Alternative 3—Complete Street: Two-lane roadway with 12-ft-wide travel lanes and a 14-ft- wide two-way center left-turn lane (total three-lane cross section). Cross section includes 5-ft-wide bicycle lanes and 10-ft-wide pedestrian space on both sides of the street. Shown in Exhibit 6-32. Exhibit 6-30. Cross section of Alternative 1—Freight Oriented. Exhibit 6-31. Cross section of Alternative 2—Freight with Bicycle Accommodations. Exhibit 6-32. Cross section of Alternative 3—Complete Street.

Project Examples 107 The exhibits show there are a few common elements across the alternative cross sections: • A two-way center turn lane to facilitate access to future industrial uses fronting 27th Avenue • Sidewalks to separate pedestrian activity and vehicle movement • One through travel lane in each direction, which was deemed sufficient given 27th Avenue will be primarily facilitating internal circulation 6.6.3 Evaluation and Selection 6.6.3.1 Estimated Performance and Financial Feasibility Authors’ Note: Sections 5.4 and 5.4.1 provide information and considerations regarding (1) how to estimate the performance of project alternatives or specific geometric design decisions and (2) how to assess the financial feasibility of those project alternatives or design decisions. Section 4.4 presents information regarding what resources are available within the profession to help conduct the performance analysis for each project alternative or geometric design decision. The performance evaluation for the alternative alignment options was based on each alignment’s ability to: • Avoid significant environmental impacts • Facilitate circulation and connections to regional transportation facilities • Maintain contiguous parcels of land for industrial uses • Create an improved alternative route to the regional park The performance evaluation for the alternative cross sections focused on the following per- formance categories and associated measures: • Safety as defined by crash frequency • Accessibility as defined by connectivity within the industrial area, connection to the regional park, connection to regional highways; and ability to accommodate large vehicles • Quality of service as defined by accommodations for bicyclists and transit riders Estimating Performance Alignment Options. The alignment options were evaluated qualitatively across the previ- ously listed attributes. The project team used geographic information system (GIS) software, aerial imagery, initial surveys, and preliminary engineering of the horizontal alignments to assess how each option performed relative to the attributes. The GIS mapping enabled the team to identify and determine the location of environmentally sensitive areas along and at the base of the hillside that need to be avoided. The identification of sensitive areas considered the physical impact of the roadway and industrial development as well as where and how stormwater runoff from 27th Avenue and the newly zoned industrial area is managed. The aerial imagery, initial survey of the industrial area, and preliminary engineering of the horizontal alignments, paired with the GIS information, enabled the project team to complete informed assessments of the alignment options. Exhibit 6-33 summarizes the qualitative assessment results for the alignment options. Each alignment option was assessed using a scale of zero to three to rate how each scored for the cri- teria above. A zero indicates the option did not meet the criteria and a three indicates the option fulfills the criteria. Alignment 3 scored the highest based on the criteria outlined previously for the following reasons: • Avoids significant environmental impacts and establishes a western border for the newly zoned area. This means incoming industrial uses and employers will only be able to develop east of 27th Avenue. This guarantees no negative impacts to the hillside and will save interested

108 Performance-Based Analysis of Geometric Design of Highways and Streets employers from having to evaluate and/or seek environmental clearance to move into the newly zoned area. • Provides a connection to US-33 in two different locations. It also provides a direct connection to I-7 on- and off-ramps. Finally, it connects with three minor arterials in the northern down- town core. One arterial is an existing bicycle boulevard and one has an existing transit line. • Provides circulation within the newly zoned area along the western and southern border. • Maintains the largest amount of contiguous parcels of land, providing potential employers with flexibility in their site development. • Provides a more direct connection and an alternate parallel route to US-33 for bicyclists to reach the regional park. Alignments 1 and 2 performed well for some of the evaluation criteria but were weakest in maintaining contiguous parcels of land for development and providing an alternate route to the regional park. Alternative Cross Sections. The performance measures associated with the performance categories identified for the alternative cross sections were estimated using the following resources: • Safety—Chapter 12 of AASHTO’s HSM (5) was used to estimate the expected safety performance. • Accessibility—Access was evaluated qualitatively based on the physical space allocated to heavy vehicles. Access with respect to connectivity within the area and to regional transporta- tion facilities was captured in the assessment of the alignment options. • Quality of Service—HCM2010 MMLOS methodology (10) was used to evaluate the quality of service (i.e., quality of the travel experience perceived by the road user) anticipated for bicyclists and transit riders. Exhibit 6-34 summarizes the evaluation results for each of the alternatives. The qualitative scale used to evaluate access was a rating of poor, fair, or good based on the degree to which the cross section is anticipated to accommodate heavy vehicles. Alignment Options Avoid Env. Significant Impact Connection to Regional Facilities Circulation within Area Contiguous Parcels of Land Improved Alternate Route to Regional Park Total Score 1 – US-33 and I-7 Access 3 2 2 1 1 9 2 – Rail Yard and Port Access 3 2 2 2 0 9 3 – US-33, I-7 and Downtown Access 3 3 3 3 3 15 Exhibit 6-33. Assessment of alignment options. Alternative Cross Sections Safety (crashes/ year) Quality of Service Access for Heavy Vehicles Bicycle MMLOS Transit Riders MMLOS 1 – Freight Oriented 2.3 E E Good 2 – Freight with Bicycle Accommodations 2.3 C C Fair 3 – Complete Street 2.3 C B Fair Exhibit 6-34. Evaluation of alternative cross sections.

Project Examples 109 As shown in Exhibit 6-34, each of the cross sections is estimated to have the same number of crashes per year even though across the alternatives there are changes in lane width, bicycle lane presence and width, and sidewalk width. The reason the expected crashes per year do not change across the alternatives is because the methodology in Chapter 12 of the HSM applicable to urban and suburban facilities is not able to quantify the safety effects of changes in lane width, presence or width of bicycle lanes, or the presence or width of sidewalks (5). This is, in part, why the project team also evaluated the quality of service for bicyclists and transit riders using the HCM2010 MMLOS methodology (10). That methodology is sensitive to the presence and width of bicycle lanes and sidewalks. Looking across the performance results of the alternative cross sections, Alternatives 2 and 3 seem to offer the more balanced options for multiple road users, while Alternative 1 clearly favors heavy-vehicle traffic. The following section discusses the financial feasibility considerations for the alternatives. Incorporating Financial Feasibility. The project team developed cost estimates for each alignment option and alternative cross section to help determine which combination to select for 27th Avenue. The cost estimates for the alignment took into consideration the length of the proposed alignment and the cost per linear foot of the alternative cross sections. The costs include considerations such as stormwater management, full-depth pavement given the antici- pated high volume of heavy vehicles, signing, pavement markings, lighting, and a contingency cost for unforeseen expenses or fluctuations in material costs. Exhibit 6-35 summarizes the cost estimates. The significant drivers of cost were the length of the alignment and width of the cross section. Alignment 3 is the longest alignment option; the cost estimates for the different cross sections for that option are greater than for Alignments 1 and 2. Similarly, Alternative 3 is the widest cross section and, therefore, across each of the alignment options has the highest associated cost. The project team did not estimate a benefit/cost ratio or calculate a cost-effectiveness factor for the different alignment options and alternative cross sections. To be able to calculate a benefit/ cost ratio or cost-effectiveness factor, simplifying assumptions would be needed to convert the assessment of alignment options into monetary benefits. Additional assumptions would be needed to quantify the degree of access provided to heavy vehicles for each alternative. The project team determined such assumptions would be vulnerable to subjectivity and may convolute the assess- ments previously performed in the project. Therefore, the city used the cost estimates in combina- tion with the performance evaluations to build internal consensus and solicit input from external stakeholders to work toward a selected alternative. Alignment Option Alternative Cross Section Estimated Cost 1 – US-33 and I-7 Access 1 – Freight Oriented $1.1 million 2 – Freight with Bicycle Accommodations $1.3 million 3 – Complete Street $1.5 million 2 – Rail Yard and Port Access 1 – Freight Oriented $700,000 2 – Freight with Bicycle Accommodations $850,000 3 – Complete Street $1.0 million 3 – US-33, I-7, and Downtown Access 1 – Freight Oriented $1.3 million 2 – Freight with Bicycle Accommodations $1.4 million 3 – Complete Street $1.6 million Exhibit 6-35. Cost estimates for 27th Avenue.

110 Performance-Based Analysis of Geometric Design of Highways and Streets 6.6.3.2 Selected Alternative Authors’ Note: Section 5.4.2 presents considerations with respect to selecting a preferred proj- ect alternative or determining the appropriate specific geometric design decisions (e.g., radius of a horizontal curve). This information helped inform the following discussion and decision. The city and project stakeholders selected Alignment 3 paired with cross-section Alter- native 2. Alignment 3 performed the best in the performance evaluation and especially well with respect to providing access to regional facilities and an alternate route for bicyclists to access the regional park. Alternative 2 was selected because it provided the most balanced means for serving heavy vehicles and bicyclists while managing cost and overall footprint of the roadway. Transit riders and pedestrians can also be served with Alternative 2 and, therefore, the city felt it was the most balanced overall solution. 6.7 Project Example 6: US-6/Stonebrook Road Authors’ Note: Project Example 6 illustrates how performance-based analysis can be integrated into the alternatives identification and evaluation stage of an interchange improvement project located in a rural area that is evolving into a suburban environment. The project example addresses considerations within a project to convert an at-grade rural intersection to an interchange. The project team initially considered potential at-grade solutions; however, as is discussed below, it ruled out at-grade options due to the desired form and function of US-6. The project team then focused on selecting the appropriate interchange form, ramp terminal intersection control type, and interchange location (e.g., spacing considerations). The learning objectives for this project example are as follows: • Demonstrate how to incorporate performance analysis into interchange-related design decisions • Illustrate the use of design resources beyond traditional design manuals [e.g., NCHRP Report 687: Guidelines for Ramp and Interchange Spacing (12)] The performance categories considered within the project example are safety and mobility. Section 4.4 helped inform the selection of the specific performance measures used to evaluate the alternative solutions. 6.7.1 Project Initiation 6.7.1.1 Project Context Authors’ Note: Using the considerations noted in Section 5.2.1, we are able to identify key characteristics of the project context that are likely to help inform the intended project outcomes, performance category, and performance measures we will use to develop and evaluate potential solutions. The following summary of the project context sets the foundation for the remaining activities within the performance-based analysis framework. An important motivation for this project is to proactively improve the at-grade US-6/Stonebrook intersection from a safety per- spective to reduce the likelihood of severe crashes by reducing conflicts and eliminating the type of conflicts contributing to severe crashes. The interchange would create new roadway capacity as the surrounding area evolves from rural to suburban land uses. US-6 is an east-west four-lane divided highway serving urban communities to the west and providing a connection to recreational mountainous areas to the east and rural agri- cultural areas further east. The state DOT is responsible for planning, implementing, and maintaining improvements to US-6. US-6 is the primary highway access to reach the mountain recreational areas and carries relatively high volumes of weekend traffic throughout the year. It also serves a relatively high percentage of heavy vehicles carrying goods to and from the devel- oped areas in the western part of the state and agricultural areas in the eastern part of the state.

Project Examples 111 Over the last two decades, development from the urban and suburban communities in the west has gradually pushed further east. As a result, there has been a higher volume of cross-street traffic at several locations along US-6 in what was once a rural and remote area. Within the last 2 years, five fatal crashes have occurred at the existing at-grade intersection at Stonebrook Road. Field observations and traffic analysis by DOT and county transportation engineers indi- cate high delay for traffic on Stonebrook Road; an increasing demand for crossing US-6 at Stonebrook Road; and high-risk movements by drivers on Stonebrook Road attempting to turn onto, turn across, or travel across US-6 (e.g., attempting to use smaller gaps in traffic on US-6). Stonebrook Road is currently a two-lane rural road with minimal paved shoulders and up to 4-ft-wide gravel shoulders in some locations. Historically, Stonebrook Road served primarily rural residents and agricultural land uses. With recent development trends, it also serves more suburban-type land uses (e.g., small strip malls, suburban residential developments) and is one of few north-south roadways that cross US-6. The US-6/Stonebrook Road intersection is within the heart of the area transitioning from rural to suburban uses. The area is experiencing the high- est growth in population, employment, and traffic volumes within the county. The study area falls within an unincorporated area of the county. The county is forecasting additional growth in the years to come as agricultural land uses transition to suburban development. The county and DOT also expect higher traffic volumes traveling to and from the recreational mountain areas as additional facilities for skiing, hiking, and other activities continue to increase. Exhibit 6-36 illustrates the existing intersection location and surrounding land use considerations. As shown in the exhibit, there is an existing interchange on US-6 west of the Stonebrook Road intersection. This is the US-6/Highway 248 (Hwy 248) interchange that currently informally indicates the approximate western extent of the denser urban and suburban development. The distance between Highway 248 and Stonebrook Road is approximately 4,550 ft. 6.7.1.2 Intended Project Outcomes Authors’ Note: The following summarizes the key information related to whom the project is intended to serve, what the project is intended to achieve (i.e., intended project outcome), the appli- cable project performance category (or categories), and the applicable performance measures. Exhibit 6-36. Existing conditions of US-6 and Stonebrook Road.

112 Performance-Based Analysis of Geometric Design of Highways and Streets Section 3.1 provides guidance and anecdotal examples of how to identify whom the project is intended to serve and what the project is intended to achieve. Sections 3.2 and 3.3 describe the over- arching relation ship and differences between defining project performance and geometric design per- formance. In this project example, the project purpose is to proactively improve the safety and mobility of the US-6/Stonebrook Road at-grade intersection in anticipation of continued evolution from sur- rounding rural uses to suburban land uses (and the corresponding increase in motor vehicle traffic). Similar to Project Examples 1 and 2, the project performance and geometric performance are relatively closely aligned. We also used Section 5.2.2 to inform the following summary of the intended project outcomes, including the applicable performance categories. In this project example, safety and mobility are the geometric performance categories of interest. We used Sections 4.4.2 (Mobility) and 4.4.5 (Safety) to select the performance measures. Given the recent growth along US-6 and continued forecasted growth in the area, the DOT would like to implement a project at the US-6/Stonebrook Road intersection that reduces the risk of serious injury and fatal crashes, improves mobility for road users on Stonebrook Road, improves connectivity from one side of US-6 to the other, and preserves the operational integrity of US-6 (i.e., minimize delay introduced for road users traveling east-west on US-6). The DOT is the primary agency stakeholder within this project because it has jurisdiction over US-6. The county is an agency stakeholder with jurisdiction over Stonebrook Road. It has the best under- standing of the forecasted growth in the area. The target audience for this project includes existing road users along Stonebrook Road and future road users within the area who desire access to both sides of US-6 as well as US-6 itself. The secondary target audience for the project is existing and future road users traveling on US-6. Road users on US-6 are primarily autos and heavy vehicles with some recreational cycling. US-6 is a state-designated bicycle route with shoulders 8 to 10 ft in width to accommodate bicyclists. Road users on Stonebrook Road include autos, heavy vehicles, agricultural vehicles, bicyclists, and pedestrians; transit service is expected to be expanded to serve the area and circulate using Stonebrook Road within a 10-year planning horizon. The purpose of this project is to identify the appropriate solutions for the US-6/Stonebrook Road intersection to serve existing and anticipated future road users. The project team identi- fied and evaluated a range of concepts and associated performance based on (1) alternatives for at-grade intersection control and grade-separated options; (2) ramp terminal intersection control, if a grade-separated interchange is selected; and (3) ramp spacing considerations on US-6 (as part of grade-separated interchange considerations). The performance categories the DOT selected are to improve intersection safety and mobility (specific to road users on Stonebrook Road). The performance measures selected for safety are crash frequency and severity. The performance measure selected for mobility is the delay experienced by traffic on Stonebrook Road. Critical qualitative considerations the DOT wanted the project team to con- sider included maintaining the operational integrity of US-6 (i.e., minimizing delay for road users on US-6) and improving connectivity across US-6 to facilitate access for anticipated land uses. 6.7.2 Concept Development 6.7.2.1 Geometric Influences Authors’ Note: We used the information presented in Section 5.3 and specifically Sec- tion 5.3.1 for guidance on how to approach identifying the geometric influences for the project. We used Section 4.4 to help inform, at a more detailed level, the specific geometric character- istics likely related to the key project performance measures. The project team initially identified three potential improvements to the US-6/Stonebrook Road intersection to improve safety and mobility. The three options were to convert the

Project Examples 113 existing two-way stop-controlled intersection to (1) traffic signal control, (2) roundabout con- trol, or (3) an interchange. While there are some operational and potential safety benefits to the traffic signal and roundabout control options, the project team decided not to pursue those improvements further due to the delay each of those options would introduce for road users on US-6. The DOT’s ultimate plan for US-6 is to create a grade-separated facility; therefore, invest- ing in at-grade intersection improvements was not of interest to the DOT. Authors’ Note: If there will be a significant delay before the interchange is constructed, there could be value, based on safety performance, in considering at-grade changes for the 8 to 10 years of benefits they might provide until the grade separation alternative could be constructed. In this project, the DOT was prepared to invest and construct grade-separated improvements within the near future; therefore, the at-grade options were not carried further in the solution development. Based on this preliminary screening, the project team focused on the following roadway attri- butes for US-6/Stonebrook Road: • Interchange Form—What type of interchange is most appropriate for the US-6/Stonebrook Road intersection? What are the safety and operational tradeoffs? • Ramp Terminal Intersection Control—What type of intersection control at the ramp ter- minal intersections on Stonebrook Road are most appropriate given safety, operational, and road user considerations? • Interchange Location/Spacing—Given interchange spacing considerations, where is the most appropriate location for the new interchange? The following presents the project team’s approach for identifying and developing solutions to address these roadway considerations. Section 4.4 provides additional guidance in identifying the design elements that influence or are influenced by a given performance measure. 6.7.2.2 Potential Solutions Authors’ Note: Section 5.3.2 provides useful information and considerations for how to develop potential solutions given the specific project context, intended outcomes, performance measures, and influential geometric elements. The project team identified a set of alternatives to address each of the three broad areas of consideration. These alternatives are as follows: • Interchange Form—Diamond, two-quadrant partial cloverleaf ramps (parclo) in advance of the cross street (Parclo A), or two-quadrant partial cloverleaf ramps beyond the cross street (Parclo B) • Ramp Terminal Intersection Control—Two-way stop, traffic signal, or roundabout • Interchange Location/Spacing—Locating the Stonebrook Road cross street and ramps in such a way as to support constructing the interchange while maintaining existing access to the areas north and south of US-6. The following subsections highlight the resources used to develop alternative solutions and the key considerations from the solution development. Resources Used to Develop Solutions. The project team used the AASHTO Green Book (1), the DOT’s roadway design manual, NCHRP Report 687 (12), the Institute of Transporta- tion Engineers’ (ITE) Freeways and Interchanges Geometric Design Handbook (13), and NCHRP Report 672 (2). Solution Development. Using these resources and considering the project perfor- mance measures, the project team developed a set of alternatives for evaluation. The follow- ing paragraphs describe key considerations in developing solutions for each of the areas of consideration.

114 Performance-Based Analysis of Geometric Design of Highways and Streets Interchange Form. The range of potential interchange forms appropriate for a given loca- tion are initially governed based on the type and function of the roadway facilities being con- nected by the interchange. In the case of US-6 and Stonebrook Road, US-6 is a highway and Stonebrook Road is a rural collector that will likely evolve into more of an urban arterial over time. US-6 is the regional facility and Stonebrook Road is a local facility providing access to US-6. Based on these functions, the interchange will be a service interchange. Using Exhibit 10-44 from the AASHTO Green Book, the project team identified potential service inter- changes including diamond, split diamond, Parclo A, Parclo B, and cloverleaf. For the US-6/ Stonebrook Road interchange, the project team decided to focus on the Diamond, Parclo A, and Parclo B interchanges as potential forms. The diamond interchange is the most intuitive for road users. Two-quadrant Parclo A and Parclo B interchanges provide flexibility to avoid right-of- way impacts to one or two quadrants of the interchange. They also have the ability to eliminate some left-turn movements at the ramp terminal intersections. Depending on the ultimate loca- tion of the interchange, this may be useful to avoid impacts to existing land uses near the US-6/ Stonebrook Road intersection. As will be discussed later, interchange forms are also influenced by the proximity and form of adjacent interchanges. Ramp Terminal Intersection Control. With each of the previously noted interchange forms, there will be two ramp terminal intersections on Stonebrook Road. The ramp terminal intersection control alternatives were initially identified as two-way stop, traffic signal, and roundabout. The current traffic volumes on Stonebrook Road do not meet volume warrants for traffic signals. Traffic volume forecasts estimate that traffic volumes will warrant a traffic signal in approxi- mately 15 to 20 years, depending on the rate of growth of surrounding development. The DOT plans to construct the improvements at the US-6/Stonebrook Road intersection within 5 years. Therefore, the project team focused on the two-way stop control (TWSC) and roundabout con- trol alternatives and compared the design life of those control forms to the estimated timeline of when the traffic signal would be warranted. The project team recognizes the TWSC would be the lowest cost control type to implement; however, it may not have the design life or anticipated safety performance associated with a roundabout. The shorter design life would require the DOT in the future to implement either a traffic signal or roundabout. If a roundabout is able to oper- ate well for near-term and long-term traffic volumes, it may be more cost effective for the DOT to invest in the roundabout ramp terminal intersections upon initial interchange construction to preclude the need to revisit the interchange 10 years after construction. Interchange Location/Spacing. NCHRP Report 687 (12) notes planners and designers focus on ramp spacing dimensions versus interchange spacing. This emphasizes the operations and safety focus on the highway mainline and ramp terminals versus the somewhat arbitrary dimen- sion between two interchanging cross streets. The project team considered various locations to construct the Stonebrook Road overcrossing. The natural location to consider is keeping Stone- brook Road on its current alignment and replacing the at-grade intersection with an interchange. However, constructing the interchange in that location creates complex traffic maintenance dur- ing construction or requires closing Stonebrook Road until the interchange can be completed. Given the importance of Stonebrook Road, closure was considered undesirable and, therefore, the team considered alternatives for relocating Stonebrook Road to create the interchange while keeping the existing intersection open during interchange construction. Locating the interchange east or west of Stonebrook Road requires considering the traffic operations, geometric design, safety performance, and signing locations. Traffic operation and safety performance is especially sensitive to ramp spacing dimensions and, therefore, the Stonebrook interchange location must be considered in the context of existing and future adjacent interchange locations on US-6. Primary Alternatives for Evaluation. Based on the project context and considerations, the primary alternatives the project team identified for evaluation are described in the following subsections.

Project Examples 115 Interchange Form Alternatives. This subsection presents schematics of the three alternative interchange forms: • Diamond Interchange: Diamond interchange providing access to and from Stonebrook Road and US-6. Shown in Exhibit 6-37. • Two-Quadrant Parclo A Interchange: Prevents right-of-way impacts in the northwest and southeast quadrants of the interchange. At the ramp terminal intersections, the Parclo A form eliminates the southbound left-turn movement to access eastbound US-6 and eliminates the northbound left-turn movement to access westbound US-6. Shown in Exhibit 6-38. • Two-Quadrant Parclo B Interchange: Prevents right-of-way impacts to the northeast and southwest quadrants of the interchange. At the ramp terminal intersections, the Parclo B form eliminates the eastbound left-turn movement from eastbound US-6 onto northbound Exhibit 6-37. Diamond interchange. Exhibit 6-38. Two-quadrant Parclo A interchange.

116 Performance-Based Analysis of Geometric Design of Highways and Streets Stonebrook Road and eliminates the westbound left-turn movement from westbound US-6 onto southbound Stonebrook Road. Shown in Exhibit 6-39. The subsection on interchange location/spacing presents where each interchange form may be most appropriate given the proximity of the Hwy 248 interchange, adjacent land uses, and desire to keep Stonebrook Road open during construction of the interchange. Ramp Terminal Intersection Control Alternatives. These three control alternatives differ in cost and longevity: • Two-Way Stop Control: The lowest cost alternative to meeting near-term traffic volume demands expected at the ramp terminal intersections. • Roundabout Control: Higher cost alternative that is able to handle near- and longer-term traffic volumes expected at the ramp terminal intersections. • Traffic Signal Control: Higher cost alternative, not warranted with current traffic volumes. Forecasted volumes estimate it will be warranted approximately 10 years after initial inter- change construction. Interchange Location/Spacing Alternatives. There are three possible alignment alternatives for the US-6/Stonebrook Road intersection: • West of Existing Stonebrook Road Intersection: This alternative locates the interchange west of the existing Stonebrook Road intersection. A key consideration for this location is that the adjacent Hwy 248 interchange is 4,550 ft from the current Stonebrook Road alignment. Based on guidance that considers conflict management and crash frequency between interchanges, this alternative would limit the potential interchange forms to a diamond interchange [see Exhibit 5-2 in NCHRP Report 687 (12)]. The minimum spacing at which a diamond inter- change form would be feasible would be approximately 4,000 ft between the Hwy 248 cross street and the new Stonebrook Road cross street. Therefore, the ramp spacing would be 1,300 ft between the US-6/Hwy 248 and new US-6/Stonebrook Road interchange ramps. The project team estimated the ramp spacing using guidance in Section 3.3.5 of NCHRP Report 687 (12). Relative to the existing Stonebrook Road cross-street location, that would provide only approximately 550 ft between the new interchange and existing Stonebrook Exhibit 6-39. Two-quadrant Parclo B interchange.

Project Examples 117 Road for constructing the on-/off-ramps for the new interchange. From a constructability perspective, that may not be sufficient space to keep the existing Stonebrook Road open to traffic throughout construction. The realignment of Stonebrook Road south of US-6 would also have the potential to negatively affect the new suburban shopping development. • Existing Stonebrook Road Interchange: This alternative locates the interchange at the existing US-6/Stonebrook Road intersection. Based on guidance from NCHRP Report 687, this alter- native would potentially allow for the parclo or diamond interchange forms [see Exhibit 5-2 in NCHRP Report 687 (12)]. Constructing the interchange at this location would not have right-of-way impacts to the new suburban shopping center southwest of US-6/Stonebrook Road or the new suburban residential development northeast of US-6/Stonebrook Road. It would be necessary to close the existing US-6/Stonebrook Road intersection during inter- change construction, which would negatively affect access to US-6 in the vicinity as well as the new land uses north and south of US-6. The drivers would need to use the US-6/Hwy 248 interchange farther west. The ramp spacing with the diamond form would be approximately 1,850 ft between the US-6/Hwy 248 and new US-6/Stonebrook Road interchange ramps. The ramp spacing with one of the parclo forms would be approximately 1,350 ft. The project team estimated the ramp spacing using guidance in Section 3.3.5 of NCHRP Report 687 (12). • East of Stonebrook Road Intersection: This alternative locates the interchange east of the existing US-6/Stonebrook Road intersection. Locating the interchange farther east enables any of the three interchange forms to be considered. It also makes it possible to maintain traffic on Stonebrook Road throughout the new interchange construction. To avoid right-of- way impacts to the new suburban residential development northeast of the US-6/Stonebrook Road intersection, this alternative would locate the new interchange approximately 2,700 ft east of the current intersection location. Therefore, the new Stonebrook Road would border the development on its eastern side. Using this alternative would require moving the main access to the residential development or constructing a local street connection from the existing main entrance to the new Stonebrook Road alignment. Shoppers or employees trav- eling to/from the new suburban shopping development would need to travel approximately a half mile east to access US-6 or cross US-6 to access land uses to the north. The ramp spac- ing would be approximately 4,550 ft between the US-6/Hwy 248 and new diamond US-6/ Stonebrook Road interchange ramps. The ramp spacing would be approximately 4,050 ft if one of the parclo forms is used. The project team estimated the ramp spacing using guidance in Section 3.3.5 of NCHRP Report 687 (12). 6.7.3 Evaluation and Selection 6.7.3.1 Estimated Performance and Financial Feasibility Authors’ Note: Sections 5.4 and 5.4.1 provide information and considerations regarding (1) how to estimate the performance of project alternatives or specific geometric design decisions and (2) how to assess the financial feasibility of those project alternatives or design decisions. Section 4.4 presents information regarding what resources are available within the profession to help conduct the performance analysis for each project alternative or geometric design decision. The performance evaluation focused on the following performance measures: • Safety as defined by crash frequency and severity • Mobility as defined by delay for road users on Stonebrook Road Estimating Performance. At the time the project team initially developed and evaluated the interchange alternatives, the HSM did not include safety prediction for freeways or interchanges. Since this project was completed, the final report for NCHRP Project 17-45, “Enhanced Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges” (14), has been made

118 Performance-Based Analysis of Geometric Design of Highways and Streets available and can be used to predict crash frequency and severity for different interchange and ramp terminal configurations. However, the final report for NCHRP Project 17-45 (14) does not include a method for predicting crashes at roundabout-controlled ramp terminal intersections. To understand the potential safety performance of the roundabout control intersection relative to the expected performance of TWSC and traffic signal control intersections, the project teamed used the results from before-after research studies published in Tables 14-3 and 14-4 of the HSM and related information published in Exhibit 5-9 within NCHRP Report 672 (2). NCHRP Report 687 (12) was used to evaluate the tradeoffs of potential interchange locations and ramp spacing considerations. HCM2010 (10) was used to evaluate the mobility tradeoffs to road users on Stonebrook Road. Additional guidance on resources for safety and mobility performance categories can be found in Section 4.4. Exhibit 6-40 summarizes the evaluation results for each of the alternatives previously presented. For each of the interchange forms, the crash estimates reflect those expected for the move- ments onto, off of, and along the ramps; the estimate does not include crashes expected at the ramp terminal intersections. Those are captured for each ramp terminal intersection type. The diamond interchange form is expected have the lowest number of crashes per year. The lower number of expected crashes per year relative to the two-quadrant Parclo A and Parclo B forms is most likely due to the lack of horizontal ramp curvature. The horizontal curvature for the Alternatives Safety (crashes/year) Mobility (avg. delay for Stonebrook Road movements) Current Year (s) Futurea (s) Interchange Forms Diamond 11.2 — — Two-Quadrant Parclo A 15.3 — — Two-Quadrant Parclo B 16.2 — — Ramp Terminal Intersections Two-Way Stop Control 5.2 12.2 >50.0 Single-Lane Roundabout 2.4 8.2 18.8 Traffic Signal 3.2 — 20.1 Interchange Location/Spacingb West of Existing Intersectionc Diamond w/ramp spacing =1,300 ft 10% to 25% more — — At Existing Intersection Diamond w/ramp spacing = 1,850 ft 0% to 10% fewer — — Parclo w/ramp spacing = 1,350 ft 10% to 25% more — — East of Existing Intersection Diamond w/ramp spacing = 4,550 ft 0% to 10% fewer — — Parclo w/ramp spacing = 4,050 ft 0% to 10% fewer — — — indicates not applicable. a 20 years after construction b Presents relative crash risk based on ramp spacing and information from Exhibit 5-5 in NCHRP Report 687. Relative crash risk is measured by the percent difference in total crashes at a given ramp spacing compared to a ramp spacing of 1,600 ft, which is the minimum ramp spacing value from the AASHTO Green Book. c Assumes a diamond interchange form given limited distance to US-6/Hwy 248 interchange. Exhibit 6-40. Alternatives evaluation of the US-6/Stonebrook Road intersection.

Project Examples 119 ramps within the two-quadrant Parclo A and Parclo B forms is associated with higher expected crashes. Delay for Stonebrook Road was not estimated for each of the interchange forms because that performance metric is directly related to the ramp terminal intersection control. The project team decided that for initial solution development and evaluation all movements occurring at the ramp terminal intersections would be subject to the control present (i.e., no free movements onto or off of US-6 on- and off-ramps). The intent is to keep vehicle speeds for vehicles depart- ing from and entering onto Stonebrook Road in the range of 25 mph because of the expected pedestrians and bicyclists on Stonebrook Road. Roundabout control at the ramp terminals is expected to perform the best with respect to the expected number of crashes per year, and it is estimated to perform relatively well with regards to existing and future mobility for road users on Stonebrook Road. Based on forecasted traffic volumes, a single-lane roundabout is expected to operate well for near- and long-term traffic volumes. The TWSC alternative performs moderately well with respect to expected number of crashes per year and existing delay for movements onto and off of Stonebrook Road. In the future years, the delay for Stonebrook Road movements with the TWSC form is notably higher than the roundabout or traffic signal control. The traffic signal control performs moderately well with respect to long-term expected crashes; this assumes it is installed after volume war- rants are met. Existing operations with a signal were not estimated because, as noted previously, with existing volumes, a signal is not warranted. Future operations with a traffic signal indicate moderate delay similar to the roundabout control. The best performing interchange location/spacing alternatives relative to crash risk are the options to locate a diamond interchange at the existing US-6/Stonebrook Road intersection and locating a diamond or two-quadrant parclo interchange east of the existing intersection. These two fundamental spacing alternatives are at the existing intersection or east of the intersection. Given the similar anticipated crash risk associated with these options, the ultimate decision will be influenced by right-of-way and access considerations for the new suburban developments in the area and the degree to which the project team determines it is critical to keep Stonebrook Road open to traffic during construction of the new interchange. Incorporating Financial Feasibility. The project team developed separate cost estimates for each interchange form, ramp terminal intersection, and interchange location/spacing configura- tion alternative. Because the detailed cost of each element is influenced by the others, the project team began by developing initial planning cost estimates for each and, in subsequent work, pre- pared more detailed cost estimates for the alternatives selected for development. The cost esti- mates shown in Exhibit 6-41 assumed that Stonebrook Road would be raised to pass over US-6, requiring a bridge to support Stonebrook Road, fill to raise Stonebrook Road approaches, and fill on which to construct the interchange ramps. The cost estimates also took into consideration items such as stormwater management needs, additional lighting, right-of-way, potential for retaining walls, and a contingency for unforeseen expenses or fluctuations in material costs. Each cost estimate assumes US-6 will maintain its current alignment and the segment of US-6 within the construction area of the interchange will be rehabilitated, repaved, and restriped as part of the overall interchange construction. The costs shown for the interchange spacing alternatives represent additional cost associated with the need to acquire right-of-way, construct additional local road connections (e.g., if the interchange is located east or west of the current Stonebrook alignment), and constructability issues (e.g., constructing temporary Stonebrook Road accesses and maintaining traffic during construction). The significant drivers of cost across the alternatives were the bridge structure, fill, and earth- work to raise Stonebrook Road above US-6. The two-quadrant Parclo A and Parclo B inter- change forms are estimated to be less than the diamond interchange form primarily because

120 Performance-Based Analysis of Geometric Design of Highways and Streets their right-of-way impacts would be constrained to fewer quadrants of the interchange. The circular ramps for the two-quadrant Parclo A and Parclo B ramps also create some opportuni- ties for on-site stormwater management treatments that are reflected as potential cost savings relative to the diamond interchange. The TWSC is the least costly intersection control in the near term. The traffic signal control has the highest cost because it requires additional roadway width on Stonebrook Road for side-by-side turn-lane storage; this requires a wider bridge across US-6. In comparison, the roundabout has a higher near-term cost relative to the TWSC intersection, but overall appears to be the more cost-effective treatment given it performs well in the near and long term for the expected growth in traffic volumes. The additional costs associated with the alternative interchange locations are primarily influenced by right-of-way acquisition needs, maintaining traffic during construction, and reconstructing the alignment of Stonebrook Road. As a result, moving the interchange west or east of the existing intersection location has higher associated costs as they have additional right-of-way, traffic maintenance, and traffic manage- ment needs and require a greater degree of reconstructing Stonebrook Road alignment. 6.7.3.2 Selected Alternative Authors’ Note: Section 5.4.2 presents considerations with respect to selecting a preferred proj- ect alternative or determining the appropriate specific geometric design decisions (e.g., radius of a horizontal curve). This information helped inform the following discussion and decision. The DOT and county selected the diamond interchange form primarily because it has the lowest expected number of crashes associated with it, is a relatively intuitive interchange form for motorists, and has the least impact to motorists traveling through on US-6. The adjacent interchange on US-6 is also a diamond form. Among the project team there was extensive discussion as to whether to locate the diamond interchange at the existing inter- section location or east of the existing intersection. Due to the higher crash risk associated with the interchange located west of the existing intersection, that option was dropped from further consideration. The primary concerns holding back selecting the interchange for construction east of the existing intersection were the access and circulation impacts Alternatives Costa Interchange Forms Diamond $24.3 million Two-Quadrant Parclo A $22.8 million Two-Quadrant Parclo B $21.2 million Ramp Terminal Intersections Two-Way Stop Control $250,000 per intersection Roundabout $600,000 per intersection Traffic Signal $350,000 per intersection Interchange Location/Spacing West of Existing Intersection $5 million Existing Intersection $3 million East of Existing Intersection $10 million a Costs shown are additive. For example, to estimate the total planning-level cost for a diamond interchange with roundabout ramp terminal control intersections located east of the existing intersection location, one would add together $24.3 million; $600,000; $600,000; and $10 million to arrive at a total planning-level cost estimate of $35.5 million. Exhibit 6-41. Cost estimates for US-6/Stonebrook Road.

Project Examples 121 to the new suburban residential development and shopping center. The DOT and county held several meetings with the new residents within the development, the developer in the process of selling the remaining homes, and the businesses within the new shopping center. Given the potentially negative impacts to the residents, developer, and shopping center businesses associ- ated with closing Stonebrook Road during the new interchange construction, the agencies and stakeholders agreed to locate the new interchange east of the existing intersection and invest in additional local road connections and realigning Stonebrook Road to facilitate access to the new residential development and shopping center with the new interchange in place. With respect to the ramp terminal intersection control, the DOT and county selected the roundabout as the preferred ramp terminal intersection control form. The roundabout’s safety and mobility performance (near and longer term), paired with its being the most cost-effective, long-term intersection form, were the primary reasons the DOT and county selected that alter- native. They also see potential for using the roundabout and landscaping to create a sense of place for and gateway to the developing area. The county, especially, sees a great opportunity for using the landscaping opportunities at the roundabouts as means for establishing a community identity that blends the rural history of the surrounding area with the forecasted growth. 6.8 References 1. American Association of State Highway and Transportation Officials. A Policy on Geometric Design of High- ways and Streets. Washington, D.C.: 2011. 2. Rodegerdts, L., J. Bansen, C. Tiesler, J. Knudsen, E. Myers, M. Johnson, M. Moule, B. Persaud, C. Lyon, S. Hallmark, H. Isebrands, et al. NCHRP Report 672: Roundabouts: An Informational Guide, Second Edition. Washington, D.C.: Transportation Research Board of the National Academies, 2010. 3. Federal Highway Administration. Low-Cost Safety Concepts for Two-Way Stop-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways. Washington, D.C.: 2008. 4. Ray, R., W. Kittelson, J. Knudsen, B. Nevers, P. Ryus, K. Sylvester, I. Potts, D. Harwood, D. Gilmore, D. Torbic, F. Hanscom, et al. NCHRP Report 613: Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections. Washington, D.C.: Transportation Research Board of the National Academies, 2008. 5. American Association of State Highway and Transportation Officials. Highway Safety Manual. Washington, D.C.: 2010. 6. Federal Highway Administration. Speed Concepts: Informational Guide. Washington, D.C.: 2009. 7. National Association of City Transportation Officials. Urban Streets Design Guide. New York, NY: 2013. 8. National Association of City Transportation Officials. Urban Bikeway Design Guide. New York, NY: 2012. 9. American Association of State Highway Transportation Officials. Guide for the Development of Bicycle Facili- ties, Fourth Edition. Washington, D.C.: 1999. 10. Transportation Research Board (TRB). Highway Capacity Manual. Washington, D.C.: Transportation Research Board of the National Academies, 2010. 11. American Association of State Highway Transportation Officials. Roadside Design Guide. Washington, D.C.: 2011. 12. Ray, B. L., J. Schoen, P. Jenior, J. Knudsen, R. J. Porter, J. P. Leisch, J. Mason, R. Roess, and Traffic Research & Analysis, Inc. NCHRP Report 687: Guidance for Ramp and Interchange Spacing. Washington, D.C.: Transpor- tation Research Board of the National Academies, 2011. 13. Institute of Transportation Engineers. Freeways and Interchanges Geometric Design Handbook. Washington, D.C.: 2005. 14. Bonneson, J. A., S. Geedipally, M. P. Pratt, and D. Lord. Safety Prediction Methodology and Analysis Tool for Freeways and Interchanges. Final Report, NCHRP Project 17-45. College Station, Texas: Texas Transporta- tion Institute, 2012.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation