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17 Transportation Networks Automobile, Bicycle, and Pedestrian Networks Automobile Network For decades, functional classification has relied upon three general thoroughfare types: arterials, collectors, and locals. More recently, arterials have been further subdivided into principal and minor, resulting in four classification types that are now in common use. Because of decades of industry familiarity with these terms and because many federal funding mechanisms are based, in whole or in part, on these four classifications, the Expanded FCS retains the same labels. The simplicity of the current functional classification is both its strength and weakness (Aubrach 2009). This simplicity has facilitated effective communication among policymakers, planners, designers, and citizens. However, this simplistic approach does not recognize all other layers, users, and functions a roadway is often called upon to fulfill. As such, it does not allow for a more complete approach in designing streets and other thoroughfares. The Expanded FCS roadway types follow basic transportation system functions and are defined based on their network function and connectivity (Figure 14). Key characteristics of each roadway type are as follows: 1. Interstates/Freeways/ExpresswaysâCorridors of national importance providing long- distance travel â Limited access. â Through traffic movements. â Primary freight routes. â Possible transit network support. â No pedestrian or bicycle traffic. â Guided by FHWA design standards. 2. Principal ArterialâCorridors of regional importance connecting large centers of activity â Through traffic movements. â Long-distance traffic movements. â Long-haul public transit buses. â Primary freight routes. 3. Minor ArterialâCorridors of local importance connecting centers of activity â Connections between local areas and network principal arterials. â Connections for through traffic between arterial roads. â Access to public transit and through movements. â Pedestrian and bicycle movements. 4. CollectorâRoadways providing connections between arterials and local roads â Traffic with trips ending in a specific area. â Access to commercial and residential centers.
18 An Expanded Functional Classification System for Highways and Streets â Access to public transportation. â Pedestrian and bicycle movements. 5. LocalâAll other roads â Direct property accessâresidential and commercial. â Pedestrian and bicycle movements. Interstates/Freeways/Expressways are not addressed in the Expanded FCS, and they are not included in the Expanded FCS matrix because FHWA design standards govern their design. The routeâs physical connectivity does not indicate the desired speed range. Rather the context itself has a greater influence on the facility speed and the associated cross section of the roadway used to guide the driversâ speed. As an example, even though a principal arterial may connect multiple cities in a region, if it traverses an urban core area, it should be designed as a low-speed urban roadway capable of accommodating all users, not a high-speed facility focused only on automobile traffic. In addition to connectivity, other factors may be used to determine the roadway type. Each of these factors is identified and discussed in the following subsections. Efficiency of Travel Trip makers traveling in a private vehicle will typically seek out roadways that allow them to travel to their destinations with as little delay as possible in the shortest amount of time. Therefore, higher-order driver facilities accommodating such travel should be planned within a network to connect major centers of activity. Route Spacing Directly related to network definition is the concept of distance (or spacing) between routes. For a variety of reasons, it is not feasible to provide high-speed facilities to accommodate every possible trip in the most direct manner possible or in the shortest amount of time. Ideally, regu- lar and logical spacing between routes of different classifications exists. High-separation-level Figure 14. Example of four-category network.
Transportation Networks 19 routes should be spaced at greater intervals than medium-separation-level routes, which are spaced at much greater intervals than low/no-separation routes. Spacing varies considerably for different areas. In densely populated urban areas, spacing of all route types is smaller and more consistent than spacing in sparsely developed rural areas. Geographic barriers greatly influence the layout and spacing of routes. Vehicle Volumes The amount of vehicle traffic, current and design year volumes, to be accommodated is another indicator of the type of facility and its functional classification (the project may either reduce or increase vehicle traffic depending on community needs and roadway system considerations). The amount of vehicle traffic affects several factors, including roadway vehicular capacity, vehicular delays, and most important, the number of lanes required to accommodate the traffic. Although the roadway project will be required to accommodate users throughout its entire design life (and, likely, beyond), many of the design choices required to accommodate traffic under a future scenario (e.g., more lanes) may be detrimental to year-of-opening conditions (for example, by encouraging higher speeds and longer pedestrian-crossing distances). Therefore, design rec- ommendations should be developed with not only opening year, future year, and intermediate operations in mind, but also an understanding of the impacts on peak and off-peak operating conditions in order to develop the âbestâ or phased-approach scenario for all users throughout the entire design life and not just the peak hour. Bicycle Network In addition to the automobile-oriented definitions of roadway type, classes for bicycles are also proposed to confer structure and priority for bicycle networks. Similar to automobile roadway-type classifications, these facilities are classified based on the network connectivity a facility provides. However, the network scale is modified to reflect shorter travel ranges. Cities have existing bicycle networks that could be incorporated into the classification system. Three classes of bicycle facilities are proposed: â¢ Citywide connector (CC)âproviding citywide connections, connections to major activity centers, or regional bicycle routes stretching over several miles that attract a high volume of use as they serve a primary commute or recreational purpose. â¢ Neighborhood connector (NC)âproviding neighborhood or sub-area connection, which establishes connections to higher-order facilities or local activity centers such as neighbor- hood commercial centers. â¢ Local connector (LC)âproviding local connections of short lengths, which provide internal connections to neighborhoods or connect to higher-order facilities. In addition to connectivity, other factors may be used in planning a bicycle network. Each of these factors is identified and discussed in the following subsections. Efficiency of Travel Trip makers will typically seek out roadways that allow them to travel to their destinations with as little delay as possible and in the shortest amount of time. Therefore, higher-order bicycle facilities should be planned within a network to connect major centers of activity by considering recreational, work/commuting, and other trip types. Mode Range Range should also be considered. The National Survey of Pedestrian and Bicyclist Atti- tudes and Behaviors Report identified an average trip length of 65 minutes, which translates
20 An Expanded Functional Classification System for Highways and Streets to 15â20 miles (NHTSA 2002). Therefore, in establishing a bicycle network, trip lengths longer than this range should factor in integration with transit facilities. Bicyclist Safety Another issue is the vulnerability of bicyclists, and facilities and options to address safe bicy- cling should be considered. This may often require greater separation between bicyclists and traffic, especially in facilities with high speeds. Route Spacing Directly related to network definition is the concept of distance (or spacing) between routes. For a variety of reasons, it is not feasible to provide high-order facilities to accommodate every possible trip in the most direct manner possible or in the shortest amount of time. Ideally, regu- lar and logical spacing between routes of different classifications exists. High-separation-level routes should be spaced at greater intervals than medium-separation-level routes, which are spaced at much greater intervals than low/no-separation routes. This spacing varies considerably for different areas. In densely populated urban areas, spacing of all route types is smaller and generally more consistent than the spacing in sparsely developed rural areas. Geographic barriers greatly influence the layout and spacing of routes. Bicycle Volumes The amount of bicycle traffic anticipated to use the facility is another indicator of the type of facility and its functional classification. Future community plans to address bicycle mobility issues and options should be considered in determining the type of facility and its functional clas- sification. The amount of bicycle traffic affects several factors, including bicycle capacity, vehicular delays, and most important, the level of risk associated within the bicycle and auto traffic mix. Three basic categories of bicycle volume are considered for categorization purposes: (1) low vol- ume, which consists of rare or occasional bicycle traffic; (2) medium volume, which has some bicycle trips (measured in bicycles per day); and (3) high volume (measured in bicycles per hour). Each of these volumes will require a different treatment based on the contextâroadway interaction. Higher-order bicycle facilities with higher volumes are considered primarily for relatively dense areas for the purposes of intermodal connection and reasonably short trips to work or shop in or between urban core, urban, and suburban areas, although rural towns may also have such networks within a smaller concentration. While rural areas do not exhibit the density typi- cally associated with successful bicycle networks, these may occur in certain circumstances. In addition, recreational users may favor longer trips and lower interruptions provided by rural roadways, and higher volumes of recreational cyclists may be found in rural areas along popular routes or near other recreational areas such as rural parks that attract cyclists. While it is desirable to develop an area-wide bicycle network plan, it is possible for bicycle facilities to be planned on a corridor-by-corridor or project-by-project basis. In pursuing this approach, it is imperative that an aerial perspective be maintained to understand how the ulti- mate network would work together to deliver a holistic solution. Pedestrian Networks While other modes readily lend themselves to a network planning strategy for incorporated areas, pedestrian activity and accommodation may be defined by the individual context of the area. This is in part because of the relatively short range of typical pedestrian activity. Moreover, pedestrian facilities may be even more localized, such as at a storefront or surrounding a bus stop, and not extend throughout the entire context area.
Transportation Networks 21 However, in denser urban areas, pedestrian activity may also cross contexts or land use boundaries, necessitating the accommodation of pedestrian traffic through a context area to another major area of activity. For example, a corridor connecting a university campus with a downtown area may require enhanced sidewalks even if the context may not demand such treatment. In addition, for larger context zones, such as suburban areas, pedestrian facilities may be focused on connecting areas of potential or anticipated pedestrian activity, such as connecting a residential subdivision to another subdivision or a nearby shopping center or transit stop (Figure 15). As such the sidewalk or path treatment may not need to continue the entire longitudinal length of the roadway but may need to have the potential to make more meaningful connections. For example, a corridor with a suburban context may not require continuous pedestrian facilities if the centers of activity with potential pedestrian traffic are discontinuous. However, where evidence of pedestrians exists or where pedestrian travel is likely expected, a minimum sidewalk width should be a priority to provide improved safety for pedestrian movements outside of the high-speed traffic area. In addition to connectivity, other factors may be used to plan a pedestrian network. Each factor is identified and discussed in the following subsections. Figure 15. Suburban area showing potential pedestrian connections between residential uses and commercial center without defined facilities along the arterial roadway.
22 An Expanded Functional Classification System for Highways and Streets Efficiency of Travel Pedestrians typically seek out roadways (paths) that let them travel to their destinations along routes they perceive as safe and interesting. Distinct from other modes, pedestrians also con- sider, but are less directed by, the route with the shortest travel time. Therefore, higher-order pedestrian facilities should be planned within a network to connect major centers of activity, considering recreational, work/commuting, and other trip types. Mode Range Range should also be taken into account. A typical pedestrian range of 0.25â0.50 mile is often used as an acceptable walking distance in the United States; however, this length may increase in urban areas where walking is the preferred method of transport (NHTSA 2002). In establishing a pedestrian network, trip lengths longer than this should factor in integration with transit and enhanced pedestrian facilities. Due to the relatively short range of pedestrian travel, the level of pedestrian activity can often be directly associated with the areaâs context and land use. Pedestrian Safety Another issue is the vulnerability of pedestrians, and facilities and options to address pedes- trian safety should be considered. Providing a separation between the pedestrian facility and the traffic, and widening the available sidewalk are methods to improve safety and pedestrian comfort by reducing potential conflicts and exposure for pedestrians. This may be especially important for roadways with medium or high speeds. Block Length The length of blocks affects pedestrian travel demand. In general, desirable block lengths range from 200â400 feet and should not exceed 600 feet (ITE and Congress for the New Urbanism 2010). Long blocks tend to discourage pedestrians. Pedestrian Volumes The amount of pedestrian traffic anticipated to use the facility will assist in determining the type of facility and its functional classification. The amount of pedestrian traffic affects several factors, including pedestrian facility capacity, vehicular delays at signalized intersections, and most important, the level of risk associated with jaywalking pedestrians. Four basic categories of pedestrian volume are used for classification purposes: (1) rare or occasional volume; (2) low vol- ume, which has a few pedestrians (measured in pedestrians per day); (3) medium volume, which has several pedestrians (measured in pedestrians per hour); and (4) high volumes (measured in pedestrians per hour and over a short time period). Each of these volumes will require a different facility based on the contextâroadway interaction. Overlays While the corridor planning/design team often directly addresses the inclusion of auto, bicycle, and pedestrian users, they may establish other user groups, such as transit and freight, to meet the unique needs of the system and the network they operate in. These user groups may then be applied to the corridor as overlays that add to the understanding of the total users for the roadway. To balance the needs of overlays, information regarding the frequency, use, and importance of the individual routes within the overlay network is essential, as discussed in the following sections. Transit Networks Transit routes are typically fixed and well-defined by the local transit agency to meet the demands of transit ridership. Additional resources are available to determine the best network
Transportation Networks 23 and routing plans for transit facilities as well as guides to aid in the design of transit facilities (AASHTO 2014). Providing additional guidance for these is beyond the scope of this report. How- ever, it is imperative to incorporate transit facilities into the overall transportation network so that they can be considered in the context of the overall transportation network and not viewed separately. Recent trends of increased ridership may require a closer examination of such transit overlays and their potential impacts on design. A close coordination with transit agencies, which typically are independent from DOTs, is essential to properly define transit overlays for roadways where transit either exists or is anticipated to be located. Freight Networks Freight networks typically describe where large trucks needing special accommodation may be concentrated on the roadway network. Studying land use to identify industrial centers and/or multi- modal ports and manufacturing and commercial areas may determine the location of freight net- works. Once freight-generating land uses are identified, preferred supply and delivery routes can be identified that connect the centers where activity originates with expected destinations. Heavy freight (i.e., large trucks) is typically routed to larger, higher classification roadways, such as major and minor arterials, where increased mobility is preferred. However, in addition to evaluating the roadway types to serve freight corridors, planners/designers should avoid sensitive context zones, such as urban and urban core areas, to minimize interactions between freight and vulnerable road users. Freight networks should be characterized based upon the frequency and size of expected freight traffic. Lower classification roadways may accommodate occasional through freight vehi- cles, while certain roadway and land use contexts may preclude large freight traffic. On heavy freight routes, the roadway, adjacent facilities, and intersections should be designed to accom- modate freight traffic and movements safely and efficiently. Moderate- or occasional-use freight facilities may marginally accommodate larger freight vehicles while being designed to provide lower speeds and shorter crossing distances for other users. Within these roadwayâcontext com- binations, operational efficiencies may be affected as freight traffic traverses the corridor. Network Overlay Application As described previously, good modal network layouts can be assembled for each user group and, once complete, may be overlaid on top of one another to develop a representation of the entire transportation network and its users (Figure 16). This is critical for identifying conflicts between user groups so that revisions may be made to best accommodate all usersânot neces- sarily on all roadways but within the entire transportation network. Incompatibilities between the needs of user groups will likely arise throughout the network planning and project development process. When these conflicts occur, an alternative network strategy can be applied to identify parallel routes with accommodations more compatible to the transportation needs of one or more of the user groups. For example, while it may be desirable to accommodate bicyclists on an arterial, heavy vehicle volumes may present a challenging trade- off decision when considering how to accommodate significant bicycle demand. In this case, parallel roads can be used to divert the bicycle traffic and establish the required separation to accommodate them. While it is easily understood that all users must be accommodated within the transportation system, all roads cannot be all things to all people. However, all users can be fully supported by the total network. It is therefore imperative that a designer evaluates the needs of all users, as well as understands the priority of users within the route and each of their nodal networks. In establishing modal networks, the primary consideration will be identifying the gen- erators for each mode and then providing a connection between major points of trip attraction While it is easily understood that all users must be accommodated within the transportation system, all roads cannot be all things to all people.
24 An Expanded Functional Classification System for Highways and Streets or generation. For instance, a roadway in the urban core with heavy pedestrian-focused retail should place a high priority on pedestrian movement as it serves as the point of attraction. Roadways connecting the activity center with either residential or transit centers may also need to prioritize pedestrian movements but may also lower priority if an alternative is identified that better accommodates the mix of users, such as establishing a pedestrian-only corridor closed to automobile traffic. At a minimum, the design should accommodate intended users on the road of concern or be moved to a parallel route. Where possible, enhancements should be made beginning with the highest priority user first. As is evident from the foregoing discussion, this application of the Expanded FCS requires expansion of the documented public transportation system to include pedestrian and bicycle networks as well as to identify future connections within these networks. Transportation agen- cies routinely establish roadway networks and clearly understand the role of these networks. On the other hand, bicyclist and pedestrian networks are not used widely and this may pose an initial issue for the Expanded FCS implementation. Due to the relatively limited range of pedestrian activity, it may not be necessary to identify a comprehensive pedestrian network, but rather the individual context of the area may be used to determine the level of pedestrian activity, with individual projects identifying special connections to transit and adjacent contexts. The longer range of bicycle travel however has the tendency to routinely pass through several context zones, increasing the need for a global network determination of bicycle facilities. This process can begin with a consultation of the appropriate stakeholders to identify existing facili- ties. For example, cities typically have an inventory of sidewalks, and bicycle groups often have bicycling maps developed for their members. Such resources can provide the basis for additional Figure 16. Overlay of transit and freight modal networks.
Transportation Networks 25 discussions with these stakeholders, aiming to identify the relative need for each facility within the respective network. This process can rely on CSS principles to define modal priorities and hence establish the network classifications for bicyclist and pedestrian facilities. An agency can follow a CSS-based approach to establish these networks: â¢ Identify appropriate stakeholders. â¢ Identify centers of activity that could attract and/or generate pedestrian and bicyclist activity. â¢ Solicit stakeholder input on route choices and priorities and collect existing maps and other data. â¢ Develop preliminary network classifications and solicit stakeholder input. â¢ Finalize and publish pedestrian and bicyclist networks. Note that the absence of a comprehensive bicycle network does not render the application of the Expanded FCS useless. As opposed to utilizing a preexisting network, a project team in con- junction with project stakeholders and public input may identify the priority of bicycle facilities for a roadway dependent upon the existing and anticipated bicycle volumes, adjacent facilities, traffic generators and attractions both within and outside the project area or along the route in question. Addressing bicycle routes in this manner will allow for advancement of modal equality; however, full network planning will be required to provide a truly cohesive system.