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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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Suggested Citation:"Chapter 2. Literature Synthesis." National Academies of Sciences, Engineering, and Medicine. 2018. Developing an Expanded Functional Classification System for More Flexibility in Geometric Design. Washington, DC: The National Academies Press. doi: 10.17226/25178.
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5 LITERATURE SYNTHESIS The purpose of this literature review is to synthesize pertinent information, specifically, to examine the purpose and need that led to the development of the FCS, and to understand current FHWA thinking and policies. Additional focus is placed on critiques and analyses of roadway classification within the modern transportation sector. It is useful to consider classification systems today in light of their original purpose and how this purpose has evolved to meet policy imperatives associated with development of the United States roadway system, especially in the second half of the twentieth century. An analysis clarifies the strong role these systems have played not only in transportation planning but also in design and programming of funds. This section presents the FCS approach and its historical background and discusses CSS issues that could potentially influence the classification system. FUNCTIONAL CLASSIFICATION SYSTEM Functional classification groups streets and highways into classes or categories based on two transportation functions of roads: mobility to and between locations and access to specific places or facilities from the road (FHWA, 1982). There are three primary classifications in the conventional system: arterial, collector, and local roads. This basic taxonomy has evolved since its first uses. For most applications, there are several subcategories, but each remains tied to a basic set of definitions for each of the three road types: • Arterials serve a primary function of vehicle mobility, generally for longer trips at a more regional scale. • Collectors serve a balance of regional and local trips and function, especially as transitions between local access streets and arterial mobility streets. • Locals are oriented primarily toward access. As a rule, they tend to be designed for lower speeds and often (though not always) a more limited range of vehicles. Figure 1 shows how arterials, collectors, and local streets balance access and mobility needs.

6 Figure 1 Mobility and access proportion of service by functional class (FHWA, 1982) This general classification has driven functional classification programs since their emergence in the mid-twentieth century. Prior to the 1920s, highways and streets in the United States were constructed largely in response to emerging economic need but were not organized into a comprehensive system. Many state transportation agencies were still in their infancy at this time and only beginning to survey comprehensive needs for statewide transportation and mobility, and they received little guidance or direct assistance from the federal government. Highway construction projects typically occurred on an incremental basis, often with significant private funding and operation. The passage of the Federal Aid Highway Act of 1921 marked the first use of a classification system to select roads that would be eligible for federal funding. It specified a relatively limited network of roads with national economic and logistical significance. After World War II, the development of the National Interstate Highway System augmented this federal-aid system and established the first comprehensive, self-sustaining funding program for highways, based primarily on revenue from taxes on motor fuels (Kane, 2003). Although implementation of this system initially focused on the construction of interstate highways, the Federal Government began to undertake an extensive effort to unite pre-existing surface highways into an overall system, which through subsequent highway funding legislation later evolved into the National Highway System (NHS) in the 1990s. This formalization of a national system led to the establishment of a more standard FCS to drive funding allocations and decisions. Functional classification was increasingly used as a

7 management tool during this period, with state transportation agencies adopting functional classification as the basis for defining statewide systems that included roads outside of those on the nationally recognized system (FHWA, 1982). In addition, professional organizations such as the National Committee on Urban Transportation and the National Association of County Engineers promoted this system as a management tool for local governments. A joint publication of the American Association of State Highway Officials (the predecessor of today’s American Association of State Highway and Transportation Officials [AASHTO]) and the National Association of County Officials and National Association of County Engineers, A Guide for Functional Highway Classification, established the FCS model that modern practitioners are familiar with and defined a framework to apply this model to needs-based planning and forecasting, project development, and programming of funds (AASHTO, 1964). The passage of the Federal Department of Transportation Act of 1966 led to a general shift in the administration of highways and roads by federal and state agencies. Two years later, the Federal-Aid Highway Act of 1968 mandated the use of a FCS, which included a study focused on the universal application of the system to all public highways and streets based on their most logical use in serving travel demands and local land uses. This study evaluated the consistency between past Federal-aid funding allocations and the development of an overall national system. This 1968 legislation and its successor, the Federal-Aid Highway Act of 1973, led to a more standard definition of classification types and a more focused understanding of the function of roads and streets. The national mandates contained in these legislative acts, which were carried out by state transportation agencies, effectively established this same system at the state level. The functional classification labeling used at the federal level today reflects an expansion of the FCS model, so that it now recognizes more precise definitions of functions within each of the three primary classes. These distinguish between access-controlled and full-access roadways, urban and rural land use and development characteristics, and major and minor (or principal and secondary) status. This expanded definition helps roadway designers distinguish between different general purposes, but more specifically differentiates roadway types eligible for Federal- aid funding assistance. This also assists in maintaining the FHWA’s Highway Performance Monitoring System (HPMS), a database that contains information on how different roads in the Federal-aid system meet stated functional purposes. As of 2010, the FCS as identified by the FHWA consists of seven basic classes: 1. Interstate Highways; 2. Other Freeways and Expressways;

8 3. Other Principal Arterials; 4. Minor Arterials; 5. Major Collectors; 6. Minor Collectors; and 7. Local Roads (FHWA, 2010a). These classifications are applied to both urban and rural areas. The urban/rural designation – while independent of a roadway’s functional classification – is a significant factor in developing both the functional classification of a road in an urban/rural context and the designated design parameters within the AASHTO A Policy on Geometric Design of Highways and Streets, commonly referred to as the Green Book, and other state guidelines. States have the option of using census-defined urban boundaries to establish urban areas, or they may adjust the census- defined boundaries to be more consistent with transportation needs. States, through coordination with local planning partners, may adjust the urban area boundaries so that fringe areas having "…residential, commercial, industrial, and/or national defense significance" (as noted in the December 9, 1991 Federal-Aid Policy Guide), are included. On October 14, 2008, FHWA issued the memorandum "Updated Guidance for the Functional Classification of Highways" which stated, "Functional classification should not automatically change at the rural/urban boundary.” Essentially this guidance allows the expansion of the urban area but does not accommodate built urban forms below population densities identified in Table 1 and 2. Table 1 U.S. Census Bureau urban area types defined by population range Census Bureau Area Definition Population Range Urban Area 2,500+ Urban Clusters 2,500-49,999 Urbanized Area 50,000+

9 Table 2 FHWA urban area types defined by population range FHWA Area Definition Population Range Allowed Urban Area Boundary Adjustments Urban Area 5,000+ Yes Small Urban Area (From Clusters) 5,000-49,999 Yes Urbanized Area 50,000+ Yes FHWA does not publish its own roadway design standards for the national system. It generally relies on the AASHTO Green Book as a central resource for guidance on design parameters (AASHTO, 2011). FHWA has adopted the 2001 Green Book as the standard for projects on the NHS. It is evident, based on standard interpretations of the AASHTO text, that the root concept of functional classification is highway-oriented. The simplicity of the FCS allows for its widespread and consistent application among states. Of particular use is the application of functional classification in network planning and design, as the system ensures network continuity and connectivity. The road function can then be useful in helping the designers understand both the function and user of the roadway when designing it. For instance, as identified in the Guide for Achieving Flexibility in Highway Design, “local roads are driven primarily by familiar drivers making repeated trips. For such facilities, designers can generally be more open to design exceptions to address or accommodate a local constraint” (AASHTO, 2004a). As a result, functional classification has been explicitly recognized as having a relationship, and thus influence, on design of roadways (FHWA, 2013). The Green Book also underscores this relationship by stating “[the] first step in the design process is to define the function of the facility is to serve...The use of functional classification as a design type should appropriately integrate the highway planning and design process” (AASHTO, 2011). The Green Book provides for flexibility in highway design and has been supplemented by other publications that emphasize context sensitive design, but many state agencies’ design manuals contain specifications that are more rigid in order to produce more uniform project outcomes (FHWA, 2010b). Over the years, functional classification has come to assume additional significance beyond its purpose as a framework for identifying the role of a roadway in moving motor vehicles through a network of highways. Functional classification carries with it expectations about roadway design, including its speed, capacity, design controls and criteria, and relationship to existing and future land use development. Federal legislation continues to use functional classification to determine eligibility for funding under the Federal-aid program. Transportation agencies describe roadway system performance, benchmarks, and targets by using functional classifications.

10 The universal application of the FCS has enabled its integration into many facets of local operations. Uses include local access management and traffic calming eligibility; grouping for operational and safety performances; and directing built form through local land use and/or zoning documents, subdivision regulations, and site development standards. The funding component of FCS almost ensures that it will be used locally, especially in jurisdictions that lack the wherewithal to develop their own system. The FHWA lists the general uses of the FCS within just the project development process as: • Program and Project Prioritization — In a climate of constrained resources, functional classification often plays a role in prioritizing expenditures. Several transportation agencies have developed separate funding programs to support the roadway systems that serve their longest distance travel, a large proportion of which comprises the Principal Arterial system. • Asset Management — Functional classification plays a role in transportation agencies' asset management programs, as agencies generally work to preserve and protect their most important assets – those that serve the most people and goods. • Safety Programs — Transportation agencies use functional classification to evaluate roadway safety and implement safety improvement programs. Agencies consider the type of roadway when evaluating the significance of crash rates. The typical safety improvement may also vary widely depending on the functional classification of a roadway. For example, speed reduction or signage improvements may be more effective in reducing crashes on a local road than on an arterial. • Highway Design — There is a correlation between functional classification and design. As an illustration, lower-class roadways have lower speed limits, narrower lanes, steeper curves, etc., while higher-class roadways have higher speed limits, wider lanes and fewer sharp curves. The relationship between functional classification and highway design is discussed in the following section. • Bridge programs — Functional classification often plays a key role in a state’s bridge program. For example, some states have set thresholds such as a functional classification of local with low traffic volume, for which one-lane bridges are acceptable. • Traffic control — Some transportation agencies may use functional class to determine the most appropriate intersection control measure.

11 • Maintenance — Functional classification often influences resurfacing cycles, which is related to asset management and project prioritization. The classification of a roadway also affects general maintenance and snow/ice removal during inclement weather. As agencies continue moving toward a more performance-based management approach, functional classification will be an increasingly important consideration in setting expectations and measuring outcomes for preservation, mobility and safety (FHWA, 2013). FUNCTIONAL CLASSIFICATION FOR STATE AGENCIES State transportation agencies have primary responsibility for transportation project development and implementation, including on the national system. As such, they have adopted policies, usually in the form of design manuals that largely follow the national-level guidance administered by AASHTO and FHWA. Many states have adopted the AASHTO Green Book design policy, whether in total or in part, for roadway projects. States with their own standards often refer to the Green Book as a general foundation for highway design guidance and may call on it for specific matters of design. A review of state design manuals was aimed at identifying the current use of the FCS and its impact on design values and elements. The review examined each manual to: 1) determine whether the state uses the existing FCS as defined by the FHWA and in the Green Book, and 2) evaluate whether the manual provides specific guidance on design element values for each of the functional classification categories as defined in the Green Book (i.e., chapters 4, 5, and 6). Forty-two state manuals were reviewed to address the two objectives noted above. The majority (38 of 42) use the same FCS for design. The exceptions are California, Connecticut, Massachusetts, and Texas. California uses a slightly different classification, where roadways are classified as freeways, expressways, highways as arterials, parkways, local streets or roads, and throughways. Connecticut uses roadside development density to refine functional classification, adopting three categories: rural open with moderate density and high density, intermediate suburban with less intense patterns of development, and built-up with typical downtown developments. Massachusetts has seized the concept of area type, which provides additional definition of the roadway context for functional classification (referred to in the manual as roadway types) and identifies three types with subcategories: urban; suburban with low density, high density, and village/town center; and rural natural, developed, and village. Texas also introduced the concept of suburban as an area type beyond rural and urban and distinguishes between two- lane and multi-lane rural roads.

12 Second, each manual was examined for whether there exists guidance for design element values in accordance to the classification system adopted. All manuals provide some guidance, provided in different formats. Some states duplicate the tables presented in chapters 4, 5, and 6 in the Green Book (e.g., Delaware, Ohio) while others summarize them in a tabular form (e.g., Maine, Tennessee, Kentucky) (Figure 2). States that have included additional categories also define design element values using both the functional classification and their additional categories. A few states (e.g., Connecticut, Indiana, and Texas) distinguish facilities based on their number of lanes and provide additional guidance based on this, while Florida imposes a similar distinction between divided and undivided. The flexibility noted for these recommendations varies among states, with some having a single value (e.g., Florida), while others have a range of desirable and minimum values for each category (e.g., Indiana).

13 Figure 2 Example of Tennessee DOT guidance

14 Several states have begun developing additional guidance policy documents for context sensitive designs, encouraging highway designers to incorporate environmental and community considerations into the interpretation of roadway design guidance. However, multiple states continue to use Green Book-based approaches that define functional classification, establish design values for each roadway component based on the its guidance, and generally offer little flexibility in terms of how these design values are to be interpreted or modified outside of a design exception or waiver process. Suburban Designation Eight of the 42 state manuals include a suburban land use category along with the commonly used urban and rural framework. This is an important distinction that acknowledges the complex transportation needs and characteristics of suburban environments. In particular, these contexts are often characterized by traffic volumes comparable to those in urban environments, although often with a much smaller supporting local street network or clear transition between arterial, collector, and local roadways. These design policy manuals also appear to acknowledge that an automobile-oriented pattern of land uses has driven local access needs throughout the roadway system, in effect keeping many roadways from truly operating in a manner consistent with the pure definition of their assigned functional classification. This applies especially to arterials, which often occupy a dual role for both mobility and access in suburban areas due, in part, to political and real estate market pressure to designate these areas for retail and commercial land uses. The speed implications of this dual function are particularly noteworthy, and design standards linked to an arterial classification (by nature oriented toward promoting mobility and throughput of traffic) are likely to emphasize higher speeds appropriate for regional arterials. These higher speeds contrast directly with the low-speed, turn-heavy travel patterns associated with local streets and access roads to private property. Design guidance that includes a suburban designation has recommended different ways of reconciling this conflict. In most policy manuals, a different set of design elements are identified for inclusion in a roadway, such as medians to assist in access management or bicycle lanes on key corridors with multimodal demand. FUNCTIONAL CLASSIFICATION SYSTEM ISSUES As the FCS has become more pervasive throughout the project development process, several issues have emerged. Many of these arise due to the application of the FCS beyond its original

15 scope and intent, as with its influence on geometric design, or through improper application by engineers and policymakers. Issues with the system are identified and discussed in the following section. Misaligned Applications One issue of concern with the FCS is that the decisions about the functional classification for a particular roadway are made typically in planning or programming stages and thus well in advance of fully understanding the project context and constraints. Classifying a roadway within a specific category occurs during the planning stages of the project based on network-wide needs and therefore represents its importance within the system-wide transportation needs of the area. But the FCS does not reflect the community goals and objectives at the local scale. Defining design elements by establishing the functional classification this early in the process runs counter to flexible and context sensitive design approaches, which gradually refine the design as the purpose and need, context, and constraints are refined throughout the entire project development process (Kirk et al., 2010). Moreover, as the FHWA (2013) established, “States should assign functional classifications according to how the roadway is functioning in the current year only.” However, this is in direct conflict with the highway design projects, which strive to meet demands for future years, whether that entails growing the system to increase the connectivity of a roadway segment or diminishing the importance of a road in the overall system because it will soon be bypassed. One of the prevailing trends of the FCS — a system originally established to organize highways by the auto traffic they are expected to accommodate — has been its linkage to geometric design standards. This has become the default position, with variations achieved through administrative waivers and the granting of exceptions. However, in some states and agencies, variations are often denied. The AASHTO Green Book provides for flexibility in highway design, and has been supplemented by other publications that emphasize context sensitive design. While design exceptions are frequently encouraged and sought out to provide balanced design features, there is a need to create a policy that establishes appropriately contextual design as the rule rather than the exception. Moreover, due to the nature of the AASHTO Green Book and state design manuals, state transportation agencies have come to depend on defined design guidelines as design standards to prevent the agency from incurring liability (Keuper, 2010). Even when street standards allow for flexibility, designer discretion, and engineering judgement, the designer often defaults to the maximum parameters for safe and efficient traffic movement (Taylor et al., 2002). With these standards often closely linked to functional classification, it has fostered a degree of

16 inflexibility in roadway design — especially in urban streets — that limits an agency’s inclination to explore multiple designs for a project. In some cases, guidance explicitly states that the design values established in these manuals are minimum values that should be met or be exceeded to achieve what is perceived the safest and most efficient design. Multimodal Design Another primary issue of concern with the FCS is its singular focus on automobile-centric travel. The FHWA’s Livability in Transportation Guidebook praises efforts to build a world class automobile travel system, though it states “we have not yet put the same effort into completing a system that works as well for walking, wheeling, or taking transit in most communities” (FHWA, 2010b). This is reinforced by the FHWA Highway Functional Classification: Concepts Criteria and Procedures, which states “Roadways serve two primary travel needs: access to/egress from specific locations and travel mobility” (FHWA, 2013). With recent refocusing on public spaces — including streets as activity centers, as well as the recent growth in pedestrian, bicycle, and transit usage for mobility — this circumscribed understanding of roadways is insufficient to provide guidance to planners and designers. CSS has raised the issue of multimodal transportation facilities and emphasized the need to conceptualize roadways as facilities that move more than vehicles (Stamatiadis, 2005). Functional classification must address the needs of other users; pedestrian, bicyclist, and transit user mobility should be included when considering the classification of roadways. Even with the focus by many states and the FHWA on CSS, priority for alternative modes of transportation is not provided. As stated by the Institute of Transportation Engineers ([ITE], 2010) recommended practice, “even with the positive “Context Sensitive Design” emphasis, AASHTO Policies in urban areas are still fundamentally in conflict with many transportation design concepts found in the New Urbanism. Pedestrian mobility, the key to New Urban walkability, is not part of the roadway’s stated purpose. The purpose of each functionally classified roadway is defined by the degree to which it serves motor vehicle mobility.” This issue becomes critical in urban and suburban areas, as right of way becomes constrained and increased pedestrian, bike, and other modal needs increase (Taylor et al., 2002). Vehicular modes typically receive priority because the FCS is so pervasive throughout the entire project development process and no equivalent system exists to dampen its influence. Some state agencies are already addressing this deficiency and have revised their functional classification schemes. For example, Idaho has incorporated the ITE recommendations in designing urban thoroughfares (ITE, 2010) and redefined their classification system to be more responsive to various users (IDOT, 2009).

17 Hall (2003) identified four key factors explaining the conflicts between the Green Book policies and walkable, New Urbanism design: 1. Functional Classification is based on motor vehicle mobility. 2. Mobility is defined based on high vehicle speed. 3. Pedestrian comfort and safety are based on low vehicle speed. 4. Widening the intersection to accommodate more travel lanes to mitigate congestion often occurs to the detriment of pedestrians and cyclists. It is therefore essential to consider the context and purpose of a roadway and to recognize how the purposes of mobility and access are served. These four factors are considered further in Chapter 4 of this report, where the objectives for a new classification system are developed. The FCS has grown in importance as a management tool since its emergence, and federal transportation funding legislation continues to use it when selecting highways and streets that are eligible for Federal-aid assistance (FHWA, 2013). The Federal-aid system is defined in federal law as encompassing the Interstate Highway System and all other public roads not classified as local roads or rural minor collectors. This demonstrates a link between federal funding and a continued agency focus on higher-level roadways, and in many cases has applied the design standards and performance criteria that transportation agencies associate with functional classes in a variety of settings. More importantly, though, this legal definition provides the foundation for a critical link to the FHWA functional classification model in any state or local roadway planning or design, meaning that this model will continue to be used for practical purposes of highway classification, even when state- or local-level policymakers attempt to incorporate a greater degree of flexibility into the process. One notable consequence of this continued reliance on the FHWA classification system is that a large share of highway funding resources continues to be concentrated on mobility-oriented corridors, even when planning occurs at a metropolitan or local level. Many of the challenges in roadway project planning and design that transportation agencies have encountered in recent years are related to the inherent conflict between access and mobility needs on arterial and collector roadways for all user groups, not just vehicles. Agencies that promote more flexible design guidance may not similarly offer funding flexibility.

18 Access vs. Mobility Those with even preliminary knowledge of the FCS will be familiar with the balancing of mobility and land access as shown in Figure 1. It should be noted however, that this figure, which has come to almost singularly define the FCS, does not appear in the most recent edition of the FHWA Highway Functional Classification Concepts, Criteria and Procedures report (FHWA, 2013). In its place, Figure 3 has been used which still illustrates the trade-off between mobility and access, but recognizes the other factors that need to be considered when roadways are classified. While this new figure at least recognizes the environment in which the roadway access-mobility dynamic takes place, it does not provide guidance on meeting or balancing those needs within the FCS. Figure 3 Access and mobility proportioning (FHWA, 2013) The focus of the FCS on mobility and access addresses longitudinal design issues (design elements that extend the entire length of the roadway). Balancing roadway speed and capacity with intersection and access control also speaks to design issues. The identification of functional priority provided by the roadway classification can assist in balancing these needs. Moreover, the identification of the functions can provide guidance when establishing system continuity of roadway networks to provide efficient flow of vehicle traffic. However, today’s designers often face more complex demands, with competing users all striving to share the same space within the cross section of the roadway. Because roadways and streets are once again seen as activity centers, they play a far greater role and serve many more functions than merely auto access or throughput. Arterials, for example, play several different roles depending on their context. In a central business district, arterials serve multiple transportation modes, while in suburban areas they tend to serve primarily autos. While the stated purpose of arterials may be to serve as key

19 mobility corridors, in practice much of the land fronting arterials is zoned for commercial uses that require numerous access points. The problem of serving this dual function illustrates one of the shortcomings of using functional classification as a primary means of network planning (ARRB, 1979). While the FCS defines streets in terms of design and operational characteristics for the movement of vehicles, classification systems can also serve as a policy framework to consider issues such as pedestrian travel, driveway access, bus routing, on-street parking, snow removal priorities, traffic signal priorities, streetscape design, and traffic management (ITE, 2010). Rural Community Issues While functional classification is essential in defining the roadway network and identifying design expectations of vehicle users, several issues can arise during application, due to its general nature and broad-brush approach. The urban/rural classification is currently essential in assigning jurisdictional roles, operational needs, and funding allocation. However, it does not provide the perspective required to guide contextual design. The AASHTO Guide in Achieving Flexibility in Highway Design (2004a) identifies this issue and notes “that a roadway’s formal classification as urban or rural may differ from actual site circumstances or prevailing conditions.” An example includes a rural arterial route passing through a small town such as that shown in Figure 4. This shows an aerial view of Salyersville, KY (population 1,800), which is bisected by US 460 – a principal arterial through town. The route may not necessarily be classified as urban, but there may be a significant segment of the road along which the surrounding land use, prevailing speeds, and transportation functions share greater affinities with urban or suburban than typical rural areas. Designers need to recognize such situations and apply common sense judgments in interpreting design criteria and developing appropriate solutions or design approaches (AASHTO, 2004a). The FHWA Flexibility in Highway Design expounds upon this concept and identifies land use as “an important determinant of the function of the area’s roads.” It further states, “the functional classification of the highway system should relate to the level of development” (FHWA, 1997).

20 Figure 4 US 460 at Salyersville, KY Urban Networks In a rural roadway system, roads typically follow a tributary nature as classified by the FCS. However, in urban areas, due to the higher density of roadways, parallel and redundant routes (especially in a grid system), the road system does not easily fit into the local, collector, and arterial hierarchy. An ARRB (1979) report noted that “Road Systems, even consciously planned ones, are not wholly tributary in nature and in much of our existing urban areas, are not tributary at all”. This is demonstrated in Figure 5 and 6. Figure 5 illustrates the road network of Lexington, KY, which is based on a hub and spoke system, and fits a generalized arterial, collector, and local system. Although within the urban core, a grid system is in place. Figure 5 Hub and spoke road network

21 Figure 6 however, shows the street system of Salt Lake City, UT, which is based entirely on a grid system. In this network, parallel and redundant routes exist for all directions. While some streets are identified as arterials or collectors, their designation is more driven by their design characteristics, i.e., number of lanes, capacity, speed, rather than their connectivity. However, many streets share design parameters and disperse traffic throughout the network, rather than concentrating traffic on a few select routes. This increases opportunities for walking and biking within the city. Figure 6 Grid road network Arising from some of these inconsistencies is the fact that classifying highways is not an exact science. The definitions used are relatively fluid and do not provide specific metrics. It should be noted though that the original intent of classification concepts was to maintain definitional flexibility, which explains why no specific metrics were included. Hall (2002) has summarized this result in stating “there is considerable indecision and ambiguity in roads serving different functions. The difficulties experienced in applying a conventionally defined hierarchy to an existing network suggest either that there are fundamental flaws in the road classification system used or that it is too ambitious to expect to define any system of classification precisely enough to serve as a basis for traffic policy”. Over the past 40 years, the practice of classification has evolved in such a manner that functional classification now functions as surrogate for determining several design element values. Some states have then inverted this process by using these metrics to assist in classifying roadways. For example, the New Jersey and Pennsylvania DOTs have identified ranges of

22 operating speeds, volumes, intersection spacing, and travel lengths for their newly developed alternative classification scheme (NJDOT & PADOT, 2008). In addition to this general guidance, they have also specified design element value ranges for each of their proposed seven classes. One can argue that the primary strength and weakness of functional classification is its simplicity (Aurbach, 2009). The FCS is a simple approach that uses vehicle access and mobility as its primary distinctions and rural/urban as its context. It is easy to understand and remember and this has provided consistent applications to fulfill network planning and funding needs. This simplicity aids in effective communication among policy makers, practitioners, and citizens. However, this simplistic approach does not recognize all of the other layers, users, and functions that a roadway must satisfy, and as such does not facilitate a holistic multimodal approach to designing roadways. One of the biggest issues is the urban/rural distinction and current use does not account for the complexity of built environments or the spectrum of land use and development types that are present from rural forests and farmlands to the urban core. Recognition of this shortcoming led to the creation of road typologies used in the Transect wherein the continuum of the land use and building density were considered to further refine and identify this complexity (Duany et al., 2003). FLEXIBILITY IN HIGHWAY DESIGN Over the past 30 years, Congress has passed a number of policy acts and regulations that have addressed the negative impacts of roadways. The Green Book has long recognized and promoted flexibility; however, many practitioners and agencies have viewed the recommended values of the Green Book as rigid standards. This is in agreement with the concept of nominal safety, where designs that are not standard-compliant are viewed as inappropriate. Practitioners guided from the nominal safety have expressed little concern for accommodating flexible designs to roadway surroundings. Moreover, they adhere to the notion that the recommendations of the Green Book have to be firmly applied, irrespective of project characteristics and location. This approach typically leads to wide swaths of pavement cutting through communities and natural resources – i.e., roadways that are not context sensitive. The public and elected officials have also become more involved and aware of the issues that roadway projects may generate and have started questioning the basis for the resulting designs. The conflict between the practitioners and the community has often resulted in delaying or stopping projects due to the competing views between these parties. It became apparent that the current approach to addressing highway design should be reconsidered, and that new means and directions for solving such conflicts needed to be identified. In the 1960s the general public

23 began to voice concerns about the adverse environmental impacts of expanding the road network. This resulted in the passage of the National Environmental Policy Act in 1969, which had significant implications for roadway design and construction. Through various activities and efforts, CSS emerged that focused on project development actions. The following sections review four efforts to address flexibility in highway design: CSS, Practical Design Solutions, Performance Based Design, and Complete Streets. Context Sensitive Solutions CSS was conceptualized to address perceived shortcomings related to design flexibility. The basic aim of CSS is to develop a project that balances the mobility, safety, environmental, and social needs. Its goal is to cultivate a project development process that provides an outcome, which harmonizes transportation requirements with community needs and values. The resulting solution should address the agency expectations to deliver an on-time and within-budget project along with the stakeholders’ expectations of addressing natural and human environment concerns and community expectations of delivering a project that will improve their quality of life. A key factor in understanding the importance of CSS is recognizing that transportation projects are unique in terms of their nature, scope, and importance of issues. While some suggest that CSS is a process, it is in fact a set of principles that are applied during the project development and delivery processes that highway agencies currently have recourse to (Stamatiadis et al., 2009). The 15 CSS principles include the following: 1. Use interdisciplinary teams. 2. Involve stakeholders. 3. Seek broad-based public involvement. 4. Use a full range of communication strategies. 5. Achieve consensus on purpose and need. 6. Address alternatives and all modes. 7. Consider a safe facility for users and the community. 8. Maintain environmental harmony. 9. Address community and social issues. 10. Address aesthetic treatments and enhancements. 11. Utilize the full range of design choices. 12. Document project decisions. 13. Track and meet all commitments.

24 14. Use agency resources effectively. 15. Create a lasting value for the community. CSS may, however, require significant changes in the focus and extent of some project development process actions. For example, adherence to CSS principles requires transportation agencies to solicit meaningful input from the public and stakeholders so that potential issues and concerns can be identified and addressed early in a project. To achieve this, all stakeholders must be identified and consulted with from the outset of a project, which may require improvement in the public involvement process. By viewing CSS as a set of principles, any agency can readily incorporate its principles into their existing project development process to bring about significant change and benefits to their organization and improve project outcomes. The ultimate goal of CSS is to deliver a project that balances the needs of safety, capacity, environment, cost, community, and other project needs, resulting in a facility that is sustainable and creates a lasting value for the community. A CSS-enlightened professional might say that it is simply a matter of doing the right thing in the right place. To help stakeholders identify what the correct course of action is, Stamatiadis et al. (2009) identified 15 distinct and actionable principles of CSS projects. These principles establish a project development process that harmonizes transportation requirements with community needs and values. Practical Design and Solutions Due to the increasing age of the United States’ transportation infrastructure and the increasing demand for travel, the need for ongoing road preservation, safety, and mobility projects has continuously increased. However, due to the financially precarious condition of most states, the availability of funds for such improvements has progressively diminished. In order to meet the challenge posed by increasing demands and limited financial resources, the planning, prioritization, and design of transportation infrastructure must be examined critically to deliver the most effective transportation system to the system users (Stamatiadis & Hartman, 2011). Typical planning and design approaches may prioritize projects at the planning and programming stage in order to best address system needs; however, infrastructure designs are then developed with the intent of delivering optimal projects. While some general financial constraints may be used, this design approach can often result in an improperly designed roadway. Such projects reduce the effectiveness of available funds. In order to fully address the needs of a city, state, or national transportation system, the current roadway design approach must be re-examined with an eye toward optimizing the entire transportation system, rather than

25 merely optimizing individual project outcomes. This approach aims to achieve a solution that would result in the maximum rate of return on the individual project and not the maximum return possible. As a result of this change in thinking, a few states have established initiatives geared toward designing more appropriately sized roadways. Most notably, the Missouri DOT has initiated a process that critically reviews projects, which has resulted in more right-sized roadways (MODOT, 2007). Missouri officials have stated that they want fewer great roads and more good roads that make a great system. This approach also allowed the DOT to address more roadway needs on a compressed schedule. To implement their approach, called “Practical Design,” officials reviewed the existing design standards and revised them in a way that addresses their concept in a new design manual. The Kentucky Transportation Cabinet has approached this issue differently. In place of minimum standards, the existing condition is established as the baseline design. A positive outcome is achieved when a project results in improvements beyond the existing conditions. The result is a disciplined planning and design approach that is not encumbered by arbitrary design guidelines, and which allows a project to achieve up to the maximum rate of return on investment (Stamatiadis et al., 2008). The primary difference between Practical Design, the term used by the Missouri DOT, and Practical Solutions, the term used by the Kentucky Transportation Cabinet, is the approach. Practical Design provides set design guidance; Practical Solutions provides principles that guide the design. The most critical component of Practical Solutions in planning and design is the definition and clarification of the initial project concept. This is the cornerstone of the project, and it significantly contains or reduces a project’s cost and impact. The idea is to develop a more efficient solution by focusing on the project needs (specific goals and objectives) rather than on stripping down components of a typical design. The concept is developed with a clear understanding of the project objectives, and designed to address those objectives while balancing project factors and elements. This approach enables a complete examination and resolution of issues instead of simply identifying elements in piecemeal fashion for cost reduction. Another focal point of Practical Solutions is how design guidelines and project needs are viewed. Rather than viewing design guidelines or performance measures as minimum thresholds that must be exceeded by the final design, Practical Solutions views them as targets for a design to achieve. Once the target is reached, increasing the investment (i.e. over-designing a project) will produce few or no additional benefits. When viewed as minimum thresholds, designs are often expanded to provide a better project, however, this often leads to improperly designed projects. Moreover, the funds spent on over-designed projects could have been directed toward other projects, which would have produced a much higher return on investment.

26 As with any project development process, the ultimate objective is to develop a project that addresses mobility, safety, community, and environmental goals. The Practical Solutions approach encourages the designer to use creative design and move away from the typical cross- section concept. Designers are frequently called upon to develop a solution that will consider and address conflicting elements by designing a roadway that balances these elements and constraints. Developing a new set of design element standards is unnecessary if Practical Solutions are to successfully realize their potential benefits. What is required is a procedure that assures that project goals/objectives are targeted using an accepted solution that balances all issues and constraints and identifies the points of diminishing returns for the project’s elements. Performance Based Design Traditionally, efforts to achieve optimal solutions through flexible design approaches, such as CSS and practical design, have been met with fears regarding liability and safety concerns. However, applications of flexible design have increased as a result of better understanding of the substantive safety concept. This is related to the introduction of performance-based analysis tools that can be used to evaluate the ultimate operational and safety performance of a geometric design. These tools include the Interactive Highway Safety and Design Model, the Highway Safety Manual (AASHTO, 2010), FHWA’s Speed Concepts: Informational Guide (Donnell et al., 2009), and the most recent edition of the Highway Capacity Manual (TRB, 2010), which includes interactive relationships between vehicle, pedestrian, and transit modes on urban corridors. Based on the availability of these tools, it is now possible to design and analyze a roadway so that individual user needs are addressed within an economically or environmentally constrained location without merely selecting minimum design elements. Complete Streets Traditional street design in the United States has focused on moving vehicular traffic, with little regard to the roadway type or surrounding context. In recent years, a more comprehensive view of transportation users has been developed. The user categories include modes that are more diverse and the design approach reflects other considerations, such as public health, air quality, climate change, and neighborhood revitalization. In response to these ideas, Complete Streets aims to create more transportation choices while maintaining safety for each. The National Complete Streets Coalition, which was established in 2005, recommends that Complete Streets be designed for the safe access and travel by pedestrians, bicyclists, motorists, transit users, and travelers of all ages and abilities (Reed & Baker, 2010). There are a

27 number of typical elements to consider when designing a Complete Street, and they may vary based on the roadway type and area context, including: pedestrian facilities (sidewalks, shared- use paths, crosswalks, median islands for refuge, pedestrian signals); bicycle facilities (paved shoulders, bicycle lanes, shared-use paths); and transit facilities (designated bus lanes, safe and accessible transit stops). Other roadway considerations include lane/median/shoulder width, turning lanes, curb extensions, and parking. The key to Complete Streets is balancing safety and convenience for the full cross-section of transportation users. SUMMARY The literature examined here indicates that FCS has assumed additional significance beyond its original purpose. While the FCS has been considered essential for defining the roadway network and identifying users’ design expectations, several issues can arise in its application, due to its general nature and broad-brush approach. Even though the urban/rural classification is essential in assigning jurisdictional roles, operational needs and funding allocation, it does not provide the perspective required to implement contextual design. For the past four decades, the FCS has anchored roadway design and project development for conventional transportation planning processes in the United States. It was intended to establish a functional framework that would enable design decisions equipped to address the full range of motorists needs for the street and road network, creating a reliable roadway system where travel purpose and roadway facility design had a clear and intuitive relationship. The FCS greatly expedited the development of the Interstate Highway and NHS and facilitated project delivery by establishing a straightforward system that let individual highway projects be analyzed and evaluated in the context of the larger transportation system. As the role of flexible design in the project development process increased — with community needs viewed through the prism of context sensitive design/solutions and economic and system performance understood through Practical Design — the need to accommodate a wider range of design parameters has become apparent. At the heart of this issue is the recognition that streets and roads play a much larger role in the community and have a far greater impact, one that reaches beyond the edges of the pavement and which addresses the competing needs of access and mobility. This includes the demand to accommodate other modes such as pedestrian, bicycle, transit and others, as well as activity zones that serve commercial centers in the roadside environment. As the FCS dictates design, both directly through policy documents such as the Green Book and individual state policies, as well as indirectly by influencing practitioners’ design choices, it is clear that the FCS falls short of addressing all these needs. This

28 is evidenced by its failure to recognize other modes of transportation, and through the limited context definition provided by the urban/rural classification. While procedures are in place to address these issues, such as the use of design exceptions, it is apparent that these are the exceptions — not the rule.

Next: Chapter 3. Existing Classification Uses »
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TRB's National Cooperative Highway Research Program (NCHRP) Web-Only Document 230: Developing an Expanded Functional Classification System for More Flexibility in Geometric Design, which documents the methodology of NCHRP Research Report 855: An Expanded Functional Classification System for Highways and Streets builds upon preliminary engineering of a design project, including developing the purpose and need.

In particular, NCHRP Web-Only Document 230 provides additional contexts beyond urban and rural, facilitates accommodation of modes other than personal vehicles and adds overlays for transit and freight.

Two case studies illustrating an application of the expanded system to actual projects are included.

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