National Academies Press: OpenBook

An Expanded Functional Classification System for Highways and Streets (2018)

Chapter: Application of the Expanded Functional Classification System

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Suggested Citation:"Application of the Expanded Functional Classification System." National Academies of Sciences, Engineering, and Medicine. 2018. An Expanded Functional Classification System for Highways and Streets. Washington, DC: The National Academies Press. doi: 10.17226/24775.
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Suggested Citation:"Application of the Expanded Functional Classification System." National Academies of Sciences, Engineering, and Medicine. 2018. An Expanded Functional Classification System for Highways and Streets. Washington, DC: The National Academies Press. doi: 10.17226/24775.
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Suggested Citation:"Application of the Expanded Functional Classification System." National Academies of Sciences, Engineering, and Medicine. 2018. An Expanded Functional Classification System for Highways and Streets. Washington, DC: The National Academies Press. doi: 10.17226/24775.
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Suggested Citation:"Application of the Expanded Functional Classification System." National Academies of Sciences, Engineering, and Medicine. 2018. An Expanded Functional Classification System for Highways and Streets. Washington, DC: The National Academies Press. doi: 10.17226/24775.
×
Page 42
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Suggested Citation:"Application of the Expanded Functional Classification System." National Academies of Sciences, Engineering, and Medicine. 2018. An Expanded Functional Classification System for Highways and Streets. Washington, DC: The National Academies Press. doi: 10.17226/24775.
×
Page 43
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Suggested Citation:"Application of the Expanded Functional Classification System." National Academies of Sciences, Engineering, and Medicine. 2018. An Expanded Functional Classification System for Highways and Streets. Washington, DC: The National Academies Press. doi: 10.17226/24775.
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39 Application of the Expanded Functional Classification System This section provides practitioners with an overview of the design concepts associated with the Expanded FCS. It describes the concepts for identifying design element considerations and tradeoffs for balancing modal needs in order to deliver a contextually appropriate multimodal design for the context and roadway-type combinations in each Expanded FCS matrix cell. The reader may also refer to the two case studies that utilize the Expanded FCS framework. Application Overview When approaching a corridor design, the design team can utilize the Expanded FCS to analyze the environment the roadway will be constructed in and the roadway network. Various user groups that must be accommodated within the roadway, often with competing needs or spatial demands, are identified also. To assist in prioritizing and balancing these needs, the importance of the project within the individual network of each road user is also highlighted. A concept that needs to be clarified from the outset is that accommodating all the users at all the times on all roadways is impossible. The following sections provide detail on how to determine: • Appropriate context category. • Appropriate roadway type. • Levels of accommodation needed for different modal users (priority and balance). • Use of network overlays such as transit and freight. • Design considerations that may assist in balancing design needs and accommodating compet- ing needs on a corridor. Each matrix cell provides a range of design options based on the defined context zone and roadway type (Figure 25). Once the context–roadway cell is identified, the modal needs and volumes must be considered to further narrow the range of design options. During this step, the needs of the driver, bicyclist, and pedestrian should be determined and examined. Lists of potential accommodations, based on the concepts defined for each user group in the previ- ous section, should be developed. Any special overlays, such as transit or freight routes, that need to be considered should be identified next. Once individual user group needs are defined, they should be synthesized to identify what design tradeoffs will be necessary to best accom- modate all users. Alternative designs should be developed and evaluated in order to deliver context-appropriate design. However, the project may extend beyond a single context, which should be addressed through the use of transition zones. NCHRP Report 737: Design Guidance for High-Speed to Low-Speed Transition Zones for Rural Highways (Torbic et al. 2012) provides additional guidance on proper transition considerations and design. Special attention needs to be paid when speed transitions from high to low and when connecting contexts with changes in modal accommodations. The project team needs to also consider potential future changes in the

40 An Expanded Functional Classification System for Highways and Streets context, for example, how community needs and goals, land use plans, and other items could have an impact on the design. Once all these individual components are selected, the cross section may be assembled and how each component can best fit within the available right-of-way needs to be determined. Available tools for evaluating different options can be used to determine the advantages and dis- advantages of each alternative. For example, Highway Capacity Manual (TRB 2016) and High- way Safety Manual (AASHTO 2010) procedures can be employed to determine the operation and safety effects of each choice; simulation can be used to determine the impacts of integrating vehicle and bicycle facilities; and Highway Capacity Manual procedures can be used to deter- mine the operational efficiency of pedestrian and bicycle facilities. Performance-based design concepts and principles can be implemented to evaluate safety and operational performance of alternatives. The designer needs to establish the metrics to use for these comparisons and develop a systematic process to evaluate each alternative and compare their impacts as they relate to the purpose and need goals and specific objectives. Single-Context Application This section describes the process for defining design choices and criteria for consideration for a few Expanded FCS matrix cells. Rural Principal Arterial Figure 26 shows an Expanded FCS matrix cell that defines the rural context for a principal arterial. In this case, a roadway provides for high-speed driving, translat- ing into high mobility and low levels of access. The appropriate facility for bicyclists is based on the class of the bicycle facility and its use. The facility for pedestrians is based on the amount of traffic anticipated, and it could be for targeted sections of the project. Finally, considerations for transit and freight will be based on the existing overlays, and their presence will have an impact on the selection of design element values. In a typical rural principal arterial, there may be rare or occasional pedestrians (Figure 27), which requires no additional design considerations. In the event that there are pedestrians, then an enhanced-width sidewalk in the form of a separate pedestrian path may be needed. The presence and volume of bicyclist traffic will dictate the sepa- ration of the bicyclist from the traffic and thus the facility to be used. Bicycle volumes are expected to increase as the bicycle network category increases from a local to a city- wide connector requiring greater separation. For local connectors, wide outer lanes with sharrows or SHARE THE ROAD signs may be appropriate due to the low bicycle vol- ume. Similarly, for a neighborhood connector, a bike lane may be appropriate, and for citywide connectors, a separate facility is preferred. In the event there is not adequate space to accommodate the high separation required for a citywide connector, the target operating speed for drivers may be revisited and adjusted (e.g., 5 mph lower) to provide a safer facility for the bicycle traffic. The presence of any transit may require minimal adjustments to the lane widths to accommodate buses if they are larger than the design vehicle selected for the facility. The same is needed if there is a freight overlay, requiring the design consideration of the typical truck that uses the facility. The presence of trucks may also have implications for shoulder widths and grades. Figure 26. Cell for a rural principal arterial from the Expanded FCS matrix. Figure 27. Relative importance of modal networks in a typical rural principal arterial.

Application of the Expanded Functional Classification System 41 Suburban Minor Arterial Figure 28 shows an Expanded FCS matrix cell that defines the suburban context for a minor arterial. In this case, a roadway provides for medium speed driving, translat- ing into medium mobility and medium levels of access. The appropriate facility to be provided for the bicyclists is based on the class of the bicycle facility and its use. The facility for pedestrians is based on the amount of anticipated traffic. Finally, design con- siderations for transit and freight will be based on the existing overlays, and their presence will have an impact on the selection of design element values. In a typical suburban minor arterial (Figure 29), pedestrian activity may be concen- trated around specific locations, and there may be a need for targeted accommodation at these locations. Possibly areas with high pedestrian traffic will exist in the vicinity of certain land uses (e.g., commercial, educational, office) that may require appropri- ate facility width commensurate with the level of pedestrian traffic. High traffic will require wide sidewalks and possibly street furniture to accommodate higher volumes. The pedestrian facility should be detached, and an appropriate buffer between the traf- fic and the pedestrians should be provided. If on-street parking is allowed or a bicycle lane is included, then the buffer could be eliminated. The bicycle network classification will also dictate the separation of the bicyclist from the traffic. As the network changes from local to citywide connector, bicycle volumes are expected to increase, establishing a need for greater separation. For local connectors, sharrows may be appropriate because of the medium vehicular speeds. Similarly, for a neighborhood connector, a bike lane may be appropriate, and for citywide connectors, a buffered lane may be considered. In the event that there is not adequate space to accommodate a buffered lane for a citywide connector, a wide bike lane may be considered as an alternative or the target operating speed for drivers may be revisited and adjusted (e.g., 5 mph lower) to provide a safer facility for the bicycle traffic. In this case, accommodating bicyclists on parallel routes could be evaluated to determine its feasibility. The presence of any transit may require adjustments to lane widths to accommodate buses if they are larger than the design vehicle selected for the facility. The same is needed if there is a freight overlay, requiring design consideration of the typical truck that uses the facility. The presence of trucks may also have implications for shoulder width and grades. Corridor Concepts The preceding discussion addressed how the Expanded FCS is equipped to handle roadway corridors that are bound within a single context. However, frequently, this is not the situation. When roadways traverse a variety of contexts, additional consideration should be given to the context transitions and the various design features to be used. Two examples are provided here to identify the issues and areas of attention. An issue that also merits attention is balancing modal needs and priorities along a corridor, because they may vary. These issues are also presented here, and they form the basis for tradeoffs among the often-competing needs of each user group in order to develop and deliver a sound, contextually appropriate multimodal solution. Example 1 The first corridor is a principal arterial transitioning contexts from rural to rural town to rural (Figure 30). The issues of concern extend beyond the accommodation of the users within each Figure 28. Cell for a suburban minor arterial from the Expanded FCS matrix. Figure 29. Relative importance of modal networks for a typical suburban minor arterial.

42 An Expanded Functional Classification System for Highways and Streets segment, as discussed previously, to providing users with the appropriate clues about changes in the roadway context and accommodating the users while they move through one context to the next. The operating target speed change from high to low for the rural to rural town transition should be communicated to drivers by more than just speed limit changes. Design features that gradually change from the rural cross section to the rural town cross section should be used to provide visual clues and positive guidance. This may involve gradual elimination or narrowing of the shoulder, narrowing of the travel lanes, use of pavement markings, and addition of gate- ways or roundabouts, or central island medians (Torbic et al. 2012). Accommodating users in the transition zone is critical. For drivers, visual clues and positive guidance for the required speed reduction need to be placed over a transition zone. For bicyclists, the first step is determining whether different bicycle facilities are in place in each zone, requiring a different level of separation. In the event that there is agreement, then the separation type could be carried forward into the transition zone and rural town context. In this case, local connectors requiring low separation could be addressed through the use of sharrows. For neighborhood and citywide connectors, a review of the separation level in the rural and rural town contexts Figure 30. Principal arterial transitioning from rural to rural town to rural context.

Application of the Expanded Functional Classification System 43 should be undertaken to identify whether there are any differences. For example, if sharrows are used in the rural setting and bike lanes are used in the rural town context, transitioning to a bike lane in the transition zone is appropriate. Obviously, similar facilities in the context areas will not require additional special consideration, but they should ensure continuity in the separa- tion level. For arterials, there is also a change in the separation level from high in the rural to medium in the rural town context. This transition requires additional considerations especially when changing from a separate multi-use path to an on-street facility. Accommodating pedestrians also follows the same considerations in the rural to rural town transition. Pedestrian facilities present in the rural town may need to be extended through the transition zone and connect with the rural context facilities. This is more significant when the enhanced-width facility in the rural context is an off-road facility, because a transition to a sidewalk would need to be provided. Transitioning from the rural town to rural context could follow a reverse order and comple- ment the rural to rural town transition. Example 2 The second example examines a minor arterial that transitions from a rural to urban context while passing through a suburban area (Figure 31). The same concerns and issues that were discussed in the previous example are applicable here as well. In this case, proper attention should be placed on how the roadway will transition from the rural to the suburban setting. Appropriate treatments could be identified to allow for the transition from high to medium operating speeds. Accommodating users in the transition area between rural to suburban contexts is critical. For drivers, visual clues and positive guidance for the required speed reduction need to be placed over a transition zone, because a large speed reduction is anticipated. For bicyclists, the first step is determining if different bicycle facilities are in place, thus requiring a different level of separa- tion. In the event that there is agreement, the separation type could be carried forward into the transition zone. In this case, local connectors requiring low separation could be addressed with the use of sharrows. For neighborhood and citywide connectors, a review of the separation level in the rural and suburban contexts should be undertaken to determine whether there are any differences. For example, if sharrows with wide lanes are used in the rural settings and bike lanes in the suburban context, then transitioning to a bike lane within the transition zone is appro- priate. Obviously, similar facilities in the two context areas will not require additional special consideration, but they should ensure continuity of the separation level. Accommodating pedestrians also follows the same considerations in the rural to suburban context transition. Pedestrian facilities present in the suburban context need to be extended, if required, through the transition zone and connect to any rural context facilities. This is again more critical when the enhanced facility in the rural context is an off-road facility, because it will need to transition to a sidewalk (minimum or wide width). Within the suburban context, pedestrian accommodation needs should be examined to deter- mine whether pedestrian accommodation will be the same throughout the corridor, or only necessary for targeted lengths of the corridor. The sidewalk width may be changed to accom- modate specific needs as the pedestrians move though the corridor. For example, initially a minimum-width sidewalk could be provided, but it could be wider approaching areas with higher activity and building density. In addition, the vehicle speed will also dictate whether the facility is adjacent or separated from the roadway. For speeds 45 mph or greater, some buffer should be provided between the pedestrian facility and the roadway.

44 An Expanded Functional Classification System for Highways and Streets For the suburban to urban transition, a set of similar considerations should be examined. Although the speed remains the same—medium for both contexts—there may be lower values used in the design element and speed limits due to higher building density and reduced setbacks. Greater reliance on positive guidance, such as use of optical narrower lanes or other treatments, is required to ensure drivers properly understand the context transitions. Bicyclist accommodation must be addressed in the transition zone, since there is the potential for a different treatment within each context. This is more important for arterials, where the separation changes from high to medium and thus may require a transition from one type of facility to another. Pedestrian facilities also need to be addressed in the transition zone, because sidewalks may need to be different widths in each context. In the urban context, high numbers of pedestrians require enhanced sidewalk treatment to account for potentially greater numbers of aggregating pedestrians. Enhanced facilities may be also needed in the vicinity of bus stops or other major points where pedestrians may congregate. In the event that speeds in the urban area are lower than 45 mph or on-street parking is allowed, then the pedestrian facilities can be adjacent to the roadway and they would not require any additional separation. Figure 31. Minor arterial transitioning from rural to suburban to urban context.

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TRB's National Cooperative Highway Research Program (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, it 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. Accompanying the report is 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.

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