Aligning Geometric Design with Roadway Context (2022) / Chapter Skim
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C-1 Appendix C: Annotated Outline of Part IV Chapters
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Aligning Geometric Design with Roadway Context Draft Part IV Annotated Outline November 2020 INTRODUCTION The Draft Part IV Annotated Outline sets the foundation for the proposed organization and content that will be in the Draft Part IV Chapters of the AASHTO Policy on Geometric Design of Highways and Streets (Green Book, 8th Edition)
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November 2020 Page 2 project to inform and influence project-specific activities that may then be guided by a project's "purpose and need." Attaining intended project outcomes could include efforts or considerations beyond roadway planning and design. These considerations are not intended to expand or inflate a given project's scope or magnitude.
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November 2020 Page 3 Green Book, 8th Edition – Overview of Parts I, II, and III Source: AASHTO Technical Committee on Geometric Design (TCGD) Part I: Introduction Chapters • CHAPTER 1: OVERVIEW • CHAPTER 2: PERFORMANCE-BASED EVALUATION CONCEPTS • CHAPTER 3: DESIGN DECISION-MAKING Key Concepts: • Guides users to concepts and principles that support flexible, multimodal design.
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November 2020 Page 4 PROPOSED ANNOTATED OUTLINE The Draft Part IV Table of Contents includes the following chapters that were adopted by the AASHTO Technical Committee on Geometric Design (TCGD)
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November 2020 Page 5 13.0 CONTEXT AND FACILITY TYPE CONSIDERATIONS 13.1 INTRODUCTION Chapter 13 serves an important function as the transition from Parts I, II, and III to context classification concepts and details of Part IV chapters. Parts I and II will integrate performance-based concepts not included or fully presented in prior Green Book editions.
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November 2020 Page 6 13.2 CONTEXT CLASSIFICATION IN THE PLANNING DESIGN PROCESS NCHRP Report 785 (Performance-based Analysis of Geometric Design of Highways and Streets) presents an performance-based approach for understanding the desired outcomes of a project, selecting performance measures that align with those outcomes, evaluating the impact of alternative geometric design decisions on those performance measures, and arriving at solutions that achieve the overall desired project outcomes.
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November 2020 Page 7 Figure 1 NCHRP Report 785 Performance-Based Design Framework The performance-based framework is founded on three basic steps: • Project Initialization -- Understanding project context and overall intended project outcomes • Concept Development -- Generate specific alternatives best suited for the given context. • Evaluation and Selection -- Using project-specific performance metrics to assess, refine, and advance the alternative.
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November 2020 Page 8 Initial Performance Attributes identified for each context classification establish the expectations of the roadway segments and nodes while also considering the project context. In addition to context classification, which generally focuses on the roadway corridor and adjacent land uses, natural environment and human influences are sometime overarching considerations.
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November 2020 Page 9 Concept Development The context classification, initial performance attributes, and natural environment and human influences can help planners and engineers understand project issues and needs that influence the consideration of potential alternatives as the project team progresses into Concept Development. Using the project context and facility type, the project team can identify initial project design elements that are most suited to align with the initial performance attributes.
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November 2020 Page 10 Selected alternatives advanced through the evaluation steps are not necessarily the alternatives selected to be approved and implemented. Depending on where a project is in the project development stage, there are other evaluations required.
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November 2020 Page 11 13.3.1 Defining Context (To be defined by NCHRP Project 15-72) NCHRP project 15-72 will define the context classifications, and Part IV Chapters (Chapters 13-19)
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November 2020 Page 12 Natural Environment and Human Influences by Context Influences Rural and Natural Areas Rural Towns Suburban Urban Urban Core Industrial, Warehouse, or Port Natural Environment Environmentally sensitive areas, high likelihood of environmental mitigation. Treating and managing environmental mitigation to address impacts.
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November 2020 Page 13 • Movement. This expectation is defined as the ability of the system to allow for the desired movements of the various user/vehicles anticipated and at predetermined volumes and patterns.
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NCHRP Project 15-77: Aligning Geometric Design with Roadway Context PN: 24769 November 2020 Page 14 Table 1 Initial Performance Attributes by Context Category Initial Performance Attributes Context Classifications Rural Rural Town Suburban Urban Urban Core Industrial, Warehouse, or Port Users/ Vehicles • Limited or no pedestrian activity. • Potential for recreational bicyclists.
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November 2020 Page 15 13.3.4 Context Temporal Considerations Project context encompasses the unique elements of the roadway along with its surroundings, environment, and community. Project context is determined by a project team through technical evaluations and engagement with the community.
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November 2020 Page 16 • Arterials • Freeways (A free or tolled controlled access facility) • Intersections o At-grade intersections o Interchanges 13.4.1 Connection to Functional Classification Section 13.3.2 creates the opportunity to establish a common vernacular and outline relationships between these important concepts.
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November 2020 Page 17 13.4.3 Segments by Facility Type Each facility type is intended to serve a role in a roadway network. A given facility type may generally have a similar role in a variety of contexts.
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November 2020 Page 18 Segment Facility Type by Context Facility Type Rural and Natural Areas Rural Towns Suburban Urban Urban Core Industrial, Warehouse, or Port Local • Low speed, low volume • Narrows streets, may be unpaved • Low speed may result in less separation between user types. • Primarily provide access to residential land uses and local destinations • Serves primarily short-distance trips • Low speed, low volume • Primarily provide access to residential land uses • Low speed, low volume • Primarily provide access to residential land uses • Network is sparse, some streets may have culde-sacs • Establishes grid system • Low speed, low volume • High access density • Serves as parallel facilities for vulnerable users • On-street parking • Connects local services to high-order streets • Low speed, moderate volume • On-street parking common • Provide access to alleys/off-street garages • May include non-motorized areas and delivery only.
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November 2020 Page 19 Segment Facility Type by Context (Continued) Facility Type Rural and Natural Areas Rural Towns Suburban Urban Urban Core Industrial, Warehouse, or Port Arterial • Serves primarily long-distance trips with an emphasis on freight traffic • High/moderate speed, moderate volumes • Emphasis on mobility with some access to larger destinations • Limited or no pedestrian activity • Potential for recreational bicyclists and high frequency of motor vehicles • Serves primarily long-distance trips connecting rural towns and cities • Mild congestion and slower traffic through built up area • Limited public and private accesses • Vehicular and bicyclist access may be provided on adjacent roadways within the network • Facilities supporting and connecting large blocks accessed by collector facilities • Facilities supporting through traffic and providing direct access to spinal development with limited supporting roadways.
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November 2020 Page 20 13.4.4 Intersections and Interchanges by Facility Type Facility types represent the roadway and intersection forms applied in a roadway network to serve the full range of user types within an appropriate range of network functions. Context classification has often emphasized cross section allocation.
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November 2020 Page 21 Intersection Feature by Context Rural and Natural Areas Rural Towns Suburban Urban Urban Core Industrial, Warehouse, or Port At-Grade • Higher speed • High truck percentages • Low to moderate speeds • Medium to high truck percentages • Mixed users • Moderate speeds • Higher volumes • Low to moderate trucks • Increased pedestrian, and bicycle features • Lower speeds • Transit stops • Increased pedestrian and bicycle features • Part of network • Low speeds • Extensive pedestrians • Transit stops and route connections • Part of network • Low to moderate speeds • High truck percentages • Longer deceleration and acceleration considerations • Longer queue storage • Larger turning radii and wider turning lanes Interchange • Wider footprint • Potential loop ramps • Integrated with topography • Wider footprint • Integrated with adjacent development • Medium footprint • Integrated with adjacent development • Narrow footprint • Higher capacity forms • Serving transit, High Occupancy Vehicles (HOV) or High Occupancy Transit (HOT)
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November 2020 Page 22 13.5.1 Project Catalyst Clearly outlining project goals and desired outcomes at the beginning of a project can help to verify that the design has a beneficial and lasting impact on the roadway. What were the key considerations that led to a project's planning and design?
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November 2020 Page 23 • Reconstruction: Reconstruction projects are those that change the basic roadway type but adhere to an existing roadway alignment. These projects may change the lane configuration or other cross-sectional elements.
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November 2020 Page 24 13.5.3 Performance Categories NCHRP Report 785 Performance-based Analysis of Geometric Design of Highways and Streets provided a range of performance metrics for consideration. They represented generalized metrics and could be a starting point for establishing project specific performance metrics desirable for a given context classification.
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November 2020 Page 25 • Mobility - the ability to move various users efficiently from one place to another using highways and streets. "Mobility" is meant to be independent of any travel mode.
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November 2020 Page 26 Quality of service may also include the perceived quality of travel by design vehicle users, such as truck or bus drivers. The quality of service may differ between a geometric solution configured to regularly serve a design vehicle and one configured to accommodate the vehicle, if necessary.
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November 2020 Page 27 • Consistency in travel time o Analyzing motor vehicle and transit operations with various levels of demand to estimate the relative consistency in travel time for various alternatives. Reliability could be a unique project performance metric and could be a differentiator in conditions where congestion does not create a difference in alternatives.
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November 2020 Page 28 13.5.4 Investment Value NCHRP Report 785 Performance-based Analysis of Geometric Design of Highways and Streets provided insights about assessing financial feasibility of a project or set of alternatives to prioritize investments and the relative effectiveness of potential projects. The intent of this consideration is to understand the relative value of various alternatives.
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November 2020 Page 29 13.6.2 Defining the Modes Modal integration is a focus element for defining context classification and creating a facility that best meets user needs. There may be temporal considerations between existing facilities and documented user types as well as future intended facility needs to serve additional or different user types.
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November 2020 Page 30 13.7.1 Design Controls This section will outline the difference between design controls and design criteria for horizontal, vertical, and cross section design. Concurrence on design controls is a first step in establish the physical roadway performance attributes that support dimensional values (criteria)
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November 2020 Page 31 • Land form and development factors that influence speed Information from NCHRP Project 15-76: Designing for Target Speed may inform content for this section. 13.7.3 Cross Section and Spatial Allocation Cross section and spatial allocation consider the available cross section and footprint to include roadways and features outside the edge of traveled way and integrated with adjacent land uses.
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November 2020 Page 32 o Intersections: Establishing features and characteristics applicable for crossing turning roadways o Interchanges: Selecting system and service forms consistent with the facility type and range of anticipated users.
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November 2020 Page 33 Segment Design Element by Context Category Design Element Context Considerations Controls Design speed • Target speed High speeds are expected in rural and natural area context. Lower speeds are expected in urban, urban core and industrial, warehouse and port contexts.
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November 2020 Page 34 Segment Design Element by Context (Continued) Category Design Element Context Considerations Cross Section Number of travel lanes • Transit only lane • Auxiliary Lanes Higher vehicular volumes typically determine the number lanes.
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November 2020 Page 35 Segment Design Element by Context (Continued) Category Design Element Context Considerations Additional Treatments/ Design Features Pedestrian crossing treatments • Spacing • Type • Curb extensions • Lighting The need for pedestrian to cross (and in closer proximity)
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November 2020 Page 36 Intersection Design Element by Context Category Design Element Context Considerations Basic Controls Intersection control type Conducting an intersection control evaluation (ICE) provides an objective approach in assessing a range of intersection control types for various contexts.
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November 2020 Page 37 Intersection Design Element by Context (Continued) Category Design Element Context Considerations Pedestrian Facilities Sidewalk and crosswalk alignments (crossing distance)
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November 2020 Page 38 Interchange Design Element by Context Category Design Element Context Considerations Basic Controls Interchange form • System interchange • Service interchange Interchanges have large footprints and modifying an existing or planning a new interchange will have major impacts on adjacent communities, especially in a built environment. For service interchange, the approaching crossing road should provide a consistent quality if service for all users based on the context.
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November 2020 Page 39 14.0 RURAL AND NATURAL AREAS 14.1 UNDERSTANDING CONTEXT Context Definition from NCHRP Project 15-72 Natural Environment and Human Influences of the Context Initial Performance Attributes for Context 14.1.1 Context Definition This section will describe how rural and natural areas often represent vast tracts of public or private land that provide a continuity to the roadway environment. Natural lands may be public or private properties that are not suitable for development for any number of reasons.
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November 2020 Page 40 o Area could include agricultural or resource areas or could include designated wilderness, forest, or parkland. o Facilities will likely include open drainage and generally blend with the natural environment.
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November 2020 Page 41 o Farm implements or equipment may represent a unique design vehicle. They be on the facility for short or longer trips or crossing the facility to access land separated by the roadway.
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November 2020 Page 42 Rural and Natural Area Modal Integration and Facility Type User Local Collector Arterial Freeway Pedestrian Co-mingle with traffic Co-mingle with traffic or on shoulder On shoulder Not applicable. Bicycle Co-mingle with traffic Co-mingle with traffic or on shoulder On shoulder Some on shoulder depending on jurisdiction Car Low volume Low volume Seasonal peaks Low volume Trucks Limited Limited.
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November 2020 Page 43 • In recreation areas, there could be a high percentage of recreational vehicles and drivers of varying degrees of experience or drivers who could be new to the area. • The lack of network or grid may result in difficulty to provide access away from the subject roadway (e.g., backage)
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November 2020 Page 44 • Longer distances at high speeds can lead to speed adaptation and transitions from high to low speeds may be more prevalent for this context. • Given natural features and constrained alignments, there could be pronounced reduced speed zones compared to other contexts.
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November 2020 Page 45 14.3.1 Project Catalyst This section will note that since traffic congestion is typically limited in rural and natural areas, common project catalysts may be a result of addressing safety performance for "state of good repair." Therefore, specific spot treatments may be considered or implemented, and during those projects other roadway or intersection issues might be addressed. With an increasing understanding of systemic safety treatments for rural roadways and intersections, project catalysts could result in a wide application of lower cost/high effectiveness treatments.
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November 2020 Page 46 o Wider impact areas associated with softer roadside grading may be possible in some areas. • Integrating pedestrian and bicycle facilities should be a consideration in planning and design even if demand is low This could include planning for but implementing the facilities at that time.
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November 2020 Page 47 There is a wide range of performance metrics associated with operating and maintaining a roadway network and its components. There are ranges of regional, state, and federal performance metrics.
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November 2020 Page 48 14.3.5 Facility Type This section will note generally there will be limited roadway networks and connectivity. • Grids could be associated with township and range section lines while local roadways and collectors could be associated with relatively isolated development patterns.
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November 2020 Page 49 This section will refer the user to appropriate GB8 Part III content on roadway design elements and how this context classification influences the choice of design values. 14.4.4 Vertical • The priority of vertical alignment varies by facility types • Aligning speed with vertical alignment • Drainage considerations This section will refer the user to appropriate Part III content on roadway design elements and how this context classification influences the choice of design values.
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November 2020 Page 50 Segment Design Element by Context Category Design Element Local Collector Arterial Freeway Controls Design speed • Target speed Design/Control Vehicle Traffic Volumes • Serving existing and forecast • Pedestrian and bicycle volumes Vehicle access points and density Terrain • rolling, level, mountainous • maximum grade Plan Horizontal alignment • Minimum radius • Spiral curve • Superelevation rate Minimum horizontal clearances Minimum sight distance • Stopping and passing sight distance Profile Vertical alignment(s) • Length of vertical curve (sag or crest)
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November 2020 Page 51 14.5 INTERSECTION DESIGN CONSIDERATIONS 14.5.1 At-Grade • Appropriately serving each user • Managing conflicts in space and time The information in the table is expected to provide design value ranges (or other supporting information) for various facility types.
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November 2020 Page 52 Interchange Design Element by Context Category Design Element Local Collector Arterial Freeway Basic Controls Interchange form • System interchange • Service interchange Type of interchange Design Vehicle Design Speed Geometry Horizontal alignment of mainline and ramps Vertical alignment of mainline and ramps Cross section of mainline and ramps Pavement cross slope and superelevation Mainline ramp gores and terminals Auxiliary lane lengths Type of intersection control at ramp termini Pedestrian Facilities at Service Interchanges Sidewalk and crosswalk alignments (crossing distance) Pedestrian ramps (including ADA)
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November 2020 Page 53 • Fit and function within overall corridor -- providing consistent crossing opportunities with a given context classification and across a range of classifications. Because rural and natural areas have limited development, this section will describe how roadway crossings may be more limited.
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November 2020 Page 54 15.0 RURAL TOWNS 15.1 UNDERSTANDING CONTEXT Context Definition from NCHRP Project 15-72 Natural Environment and Human Influences of the Context Initial Performance Attributes for Context 15.1.1 Context Definition This section will describe how rural towns could include villages, towns, or small cities that arise in relative isolation as well as areas with concentrated development over a short distance; meaning they could be discrete development patterns and communities connected with rural or natural area context roadways. The towns may primarily be situated on the main roadway with core or center that could include transitional development on the fringe.
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November 2020 Page 55 o Separated roadways could have vegetated medians. o Natural features and topographic elements could constrain town development and roadway cross section.
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November 2020 Page 56 15.2.1 Users/Vehicles This section will describe the users/vehicles expected in a rural town context. It will note there will be increased emphasis on various users.
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November 2020 Page 57 o There will be pedestrians crossing roadways include students who use school buses and possible transit or paratransit users. Modal connectivity and transitions between land uses could be an important planning and design consideration.
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November 2020 Page 58 15.2.3 Permeability This section will address the types of access -- public or private -- expected and note that rural town access has special consideration for the differing motorist expectations for through and local traffic. • High variations in minor street to primary street access may result in difficult side street or driveway movements during peak periods.
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November 2020 Page 59 o Similarly, an arterial serving through trips will likely need to serve short distance trips with development access directly accessing the arterial. • Missing network elements lead to point loading of certain facilities.
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November 2020 Page 60 o During non-peak periods, roadway and intersection capacity may not be a focus. Quality of service and completeness of sidewalk facilities could be a focus.
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November 2020 Page 61 o For rural towns, this could mean including pedestrian and bicycle facilities that had not been a perceived need previously. • Contemporary planning and design could include applying design criteria that reflects progressions in the profession.
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November 2020 Page 62 • As the community may identify with specific character elements, the metrics should lead to roadway and intersection design features that support that community interest. o For example, if a town has a commercial or tourist element, parking and pedestrian facilities could be focus supported by lower motor vehicle speeds on the main roadways.
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November 2020 Page 63 • Freeways are likely lower volume and higher speed with independent vertical and horizontal roadway alignments. • Intersections and service interchanges ramp terminal intersections are commonly configured to primarily serve motorized users; however, the rural town land uses encourage more walking and biking and non-motorized users should be included in planning and design decisions, particularly at intersections.
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November 2020 Page 64 15.4.5 Cross Section • Prioritizing design elements • Quality of service for each user • Environmental and community effects associated with project footprint Given the likely land use development in a rural town, there will likely be at least some need for curb and gutter sections. This section could focus on the appropriate cross section design transition needs into and out of the rural town and methods to consider and attain footprints that do not adversely impact roadside development.
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November 2020 Page 65 16.0 SUBURBAN 16.1 UNDERSTANDING CONTEXT Context Definition from NCHRP Project 15-72 Natural Environment and Human Influences of the Context Initial Performance Attributes for Context 16.1.1 Context Definition This section will describe how suburban roadways can serve residential, commercial, and light industrial or warehouse development. The development patterns can be mixed with various land uses on either side of a primary roadway.
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November 2020 Page 66 • Commercial areas may be significant trip generators increasing the number of turning vehicles on and off the suburban roadways. These areas attract pedestrians so roadway and intersections configurations must consider and account for and counter potential user conflicts.
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November 2020 Page 67 • Social Demographics o There could be varying social demographics along suburban arterials. Depending land use patterns there could be diverse populations or special transportation dependencies or equity considerations.
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November 2020 Page 68 • Trucks serving long distance freight needs may be passing along the suburban roadways to freeway interchanges. • There could be increased freight delivery and trucks on the facilities and turning to and from roadways.
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November 2020 Page 69 o While non-motorized volumes may be low compared to motorized users, the safety performance and quality of experience of these users should remain a high priority. Given the range of development and the role of each type of facility in this context classification, each facility type (local, collector, and arterial)
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November 2020 Page 70 o Roadway cross sections must consider pedestrian features, including pedestrian focused lighting levels along and crossing the roadways. • Bicyclists o Traffic volumes and patterns on lower order streets may vary greatly depending on the type of land uses.
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November 2020 Page 71 16.2.2 Movement This section acknowledges that non-motorized users are going to be affected by traffic volume as well as composition and proximity to the suburban roadways. Residential areas may have limited street lighting, and roadway crossing visibility could be a focus for quality of service and safety performance.
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November 2020 Page 72 • High variations in minor street to primary street access may result in difficult side street or driveway movements during peak periods. • Consider locating and designing access points to maximize intersection and stopping sight distance.
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November 2020 Page 73 • Residential areas may have roadway network serving the neighborhood uses but limited connectivity from that area. This can result in longer trips or out of direction travel for users who wish to access commercial areas and other services.
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November 2020 Page 74 This section will note how a limited network puts more emphasis on the remaining roadways and intersections. It could highlight how regional highways connecting to other suburban roadways create specific volume and user needs that must address longer distance connectivity while meeting the desired quality of service on suburban roadways.
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November 2020 Page 75 • With limited horizontal and vertical alignment features to manage speeds, traffic speeds on arterials could be greatly affected by signal systems and assumed running speeds and signal timing. • It would note the importance of considering speed and cross section and pedestrian crossing safety.
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November 2020 Page 76 Suburban roadways can be in areas of continual transition. Legacy developments that were at one time separated from other communities can become connected to incremental development over time.
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November 2020 Page 77 o This may include reducing curb radii to support pedestrian crossings, narrowing travel lanes, or adding crossing treatments or medians. o Integrating bicycle travel or pedestrians could lead to considerations of adding mixed use facilities, bicycle lanes, or parallel separated facilities.
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November 2020 Page 78 There may be special consideration of removing barriers and creating pedestrian and bicycle facility connections between different land uses in this context area. Early project multimodal, freight, and emergency response planning can help guide the types of treatments on a given roadway in later project development stages.
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November 2020 Page 79 • Light industrial and warehousing areas may include access to railroads and suburban roadways could require special freight access considerations. • Traffic operations and mobility may be a more significant metric than other contexts and there should be considerations of what levels of congestion may be acceptable avoid overbuilt roadways during non-peak conditions.
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November 2020 Page 80 • Arterials will likely be limited to those roadways serving longer trips, connecting communities. • Freeways are likely moderate volume and with increased congestion associated with traffic peaks.
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November 2020 Page 81 It will reflect that suburban roadways serve an array of land use types, and the horizontal alignment and supporting design elements should be based on attaining speeds appropriate for each land use form within the suburban context. 16.4.4 Vertical • The priority of vertical alignment varies by facility types • Aligning speed with vertical alignment • Drainage considerations Given a likely reduced intended operating speed, vertical design may have limited emphasis for operations and may be more target to drainage considerations.
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November 2020 Page 82 16.5 INTERSECTION DESIGN CONSIDERATIONS This section will include a table that describes the range of various intersection (at-grade and grade separated) design elements by facility type in a Suburban Context.
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November 2020 Page 83 17.0 URBAN 17.1 UNDERSTANDING CONTEXT Context Definition from NCHRP Project 15-72 Natural Environment and Human Influences of the Context Initial Performance Attributes for Context 17.1.1 Context Definition This section will describe how urban roadways can serve a mixture of uses that are typically within a well-connected road network. There may be layers of development off a main road that transition from a mixture of office, commercial, retail, and other uses to residential neighborhoods that could include multifamily and contiguous areas of single-family dwellings.
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November 2020 Page 84 The section will note how urban roadways can serve development patterns that are relatively consistent and contiguous. Urban roadways could serve relatively small development tracts of various land uses that can include parks and open space and civic centers or entertainment venues that generate pedestrian and bicycle users.
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November 2020 Page 85 • Social Demographics o There could be varying social demographics along urban arterials. Depending on land use patterns, there could be diverse populations or special transportation dependencies or equity considerations.
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November 2020 Page 86 • Arterial streets or street pairs could serve as a "main street" creating friction associated with on street parking and increased side street intersections. • Large truck percentages will generally be low.
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November 2020 Page 87 • Transit service is common on urban roadways, and special consideration is needed for integrating transit stops, transit centers, and pedestrian routing to and from transit service. • Traffic volumes and patterns on lower order streets may support needs to have separated pedestrian/bicycle facilities on lower order streets to provide and appropriate quality of service for those users.
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November 2020 Page 88 The table will note that modal integration considerations are like the natural environment and human influences in Section 17.1.2. It will emphasize the role of diverse vehicle composition and travel patterns and associated land use activities on urban roadways and intersections.
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November 2020 Page 89 Transit quality of service can be affected by the type of bus stop provided and the use of bus pull outs or curbed bulb outs. Transit user quality of service can be affected by locations of intersection near or far side stops and potential out-ofdirection walking distances.
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November 2020 Page 90 Urban roadways typically having more complete networks means there are potential alternate routes. This creates opportunities for addressing the needs and demands of the primary roadway via the available network.
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November 2020 Page 91 • Given increased range of activity for all users, speed transitions to the urban street system is vital because of the increased presence of pedestrians, bicyclists, and turning vehicles. • Urban roadway intersections should be configured to specifically create a more comfortable and safe experience for vulnerable users.
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November 2020 Page 92 17.3.1 Project Catalyst This section will note that project catalysts can vary from maintenance activities and upgrades associated with signalization, paving, reallocating roadway cross section to include bicycle lanes, and other reconstruction associated with utilities. There may be fewer larger scale capacity enhancements and more optimization or user integration projects.
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November 2020 Page 93 • This may include reducing curb radii to support pedestrian crossings, narrowing travel lanes, or adding crossing treatments or medians. • Integrating bicycle travel or pedestrians could lead to considerations of adding mixed use facilities, bicycle lanes, or parallel separated facilities.
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November 2020 Page 94 17.3.3 Project Development Stage This section will connect network planning and program and note how early network and system planning can help determine where and how considerations for freight routes or bicycle/pedestrian networks can guide planning and design of urban roadways. Transit is common in environments for urban roadways and supporting sidewalk and crossing locations become a needed planning and design focus.
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November 2020 Page 95 Roadways serving residential areas should operate at low speeds and serve users expected in that environment. There may need to be special consideration for the connections and treatments between roadways in the residential areas compared to roadways serving adjacent commercial areas.
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November 2020 Page 96 • There be a network or grid patterns that lead to a fuller use of collector and local street types. • There will likely be an extensive parallel and crossing urban arterial roadways potentially resulting in large intersections.
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November 2020 Page 97 17.4.2 Evaluating the Project Limits and Transitions This section will discuss how potentially higher speeds approaching urban roadway could lead to special needs for transitions to and from roadways between contexts. This could include addressing needs to transition between higher speeds of suburban roadways to slower speeds urban.
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November 2020 Page 98 17.4.7 Segment Design Elements This section will include a table that describes the range of various segment design elements by facility type in an urban context. An example of this table is shown in Section 14.4.7.
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November 2020 Page 99 18.0 URBAN CORE 18.1 UNDERSTANDING CONTEXT Context Definition from NCHRP Project 15-72 Natural Environment and Human Influences of the Context Initial Performance Attributes for Context 18.1.1 Context Definition This section will describe how urban core roadways can serve a mixture of uses that are typically within a well-connected road network. There will be a broad mixture of office, commercial, retail, and other uses on a well-connected roadway network.
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November 2020 Page 100 Freeways may be below, at-grade, or elevated. They typically have a narrow, confined footprint with walls at the right-of-way line.
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November 2020 Page 101 o There are typically few natural environment considerations associated with urban core roadways. Greenspace and natural areas may be designated parks or greenways and open spaces associated with adjacent lakes, canals, or rivers.
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November 2020 Page 102 • Permeability: High access opportunities for pedestrians. Medium access opportunities for vehicles and less confident bicyclists who are not comfortable comingling with motor vehicle traffic • Network: Cohesive and dense surrounding street network with multiple parallel and cross streets.
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November 2020 Page 103 • Likely increased and localized extensive pedestrian activity associated with development patterns and special focus for intersection design and pedestrian crossings. • Pedestrians may dominate street crossings and impede motor vehicle traffic at times.
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November 2020 Page 104 Include considerations for addressing freight and delivery needs including intersection curb radii. Curb radii should be customized to meet the design vehicles intended while accommodating more rare and larger trucks that may serve and area.
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November 2020 Page 105 18.2.2 Movement This section acknowledge non-motorized users are going to be affected by traffic volume and composition and proximity to the urban roadways. Non-motorized user numbers decrease the dominance and focus of serving motor vehicle traffic.
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November 2020 Page 106 • Urban core roadways will typically be part of a connected system that results in a viable roadway network or grid. There may be needs to the full network to create access and circulation opportunities for pedestrians, bicyclists, freight, and emergency responders to avoid having to pass through other high demand roadways or intersections • Considering overall access and circulation could guide planning and design choices on the primary and secondary roadways.
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November 2020 Page 107 18.2.5 Speed This section will explain speeds are expected to be slow and the slow speeds are not so influenced by roadway geometric design but by the sheer volume of activity and friction occurring in the urban core network. • Traffic speeds on all urban core roadways could be greatly affected by signal systems and signal timing.
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November 2020 Page 108 This section will address how projects may lead to discrete or focused solutions. These may be villages or districts or centers that demonstrate a specific character or theme.
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November 2020 Page 109 • Because of the users' needs associated with various land uses within the urban core context, integrating pedestrian and bicycle facilities should be a primary consideration. • Adding pedestrian scale lighting in enhanced pedestrian crossing treatments may be part of roadway and intersection planning.
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November 2020 Page 110 As the community may identify with specific character elements, the metrics should lead to roadway and intersection design features that support that community interest. Roadways serving residential areas should operate at low speeds and serve users expected in that environment.
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November 2020 Page 111 18.3.5 Facility Type This section will note generally there may be well developed roadway networks and connectivity. This connectivity increases route choices and opportunities to serve users across the urban core roadway network.
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November 2020 Page 112 18.4.1 Three-Dimensional Design Element Context Considerations This section will emphasize the design focus on slower speed and broader range of users in the urban core context. It will note how the urban core roadway facilities should support nonmotorized users and optimize the quality of service and safety performance for each facility type.
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November 2020 Page 113 It will discuss the need for overall consistency in serving each user while noting serving each user at an applicable quality of service means adapting the urban core roadway forms to meet those needs. 18.4.7 Segment Design Elements This section will include a table that describes the range of various segment design elements by facility type in an urban core context.
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November 2020 Page 114 19.0 INDUSTRIAL, WAREHOUSE, OR PORT 19.1 UNDERSTANDING CONTEXT Context Definition from NCHRP Project 15-72 Natural Environment and Human Influences of the Context Initial Performance Attributes for Context 19.1.1 Context Definition This section will describe how roadways in an industrial, warehouse, or port context classification will primarily provide access to specific destinations. This context will typically have high levels of truck activity and the truck percentage is likely to be high as a proportion of the overall traffic volume.
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November 2020 Page 115 This section will identify the generalized expectations typically associated with the Industrial, Warehouse, or Port context classification. For the five categories identified in Chapter 13, these expectations are summarized below and discussed in greater detail in the following subsections.
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November 2020 Page 116 19.2.4 Network This section will describe the role of each facility type in the industrial, warehouse, or port context classification. Off-site network considerations focus on keeping truck traffic on designated routes.
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November 2020 Page 117 19.3.2 Project Types New Construction Focus on providing horizontal, vertical, and cross section design features consistent with contemporary safety and operational performance needs. There are fewer opportunities for new construction and design flexibility needs increase in this context.
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November 2020 Page 118 There may be a focus traffic operations and accounting for heavy truck volumes through intersections. 19.3.5 Facility Type This section will note the focus of planning and design will be to serve large volumes of heavy vehicles.
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November 2020 Page 119 Vertical design will likely be limited to meeting drainage considerations and providing roadway profiles that have adequate vertical clearance to overhead signs and bridges. 19.4.5 Cross Section • Prioritizing design elements • Quality of service for each user • Environmental and community effects associated with project footprint The focus will be providing width for truck tracking and lane discipline.
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Key Terms
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