This chapter provides principles and guidance for the design of a thoroughfare's traveled way, which includes the elements between the curbs such as parking lanes, bicycle lanes, travel lanes and medians. The traveled way also includes midblock bus stops and midblock crosswalks. The guidance in this chapter is used in conjunction with the guidance for the other two thoroughfare components—the streetside (Chapter 8) and intersections (Chapter 10).
1. Introduces and defines the elements of the traveled way;
2. Presents traveled way design considerations, including key factors in determining cross-sections;
3. Describes principles for transitioning urban thoroughfares when there is a change in context, thoroughfare type, or geometric elements; and
4. Provides design guidance for the primary elements of the traveled way, which are lane width, medians, bicycle lanes, on-street parking, geometric transition design, midblock crossings, pedestrian refuge islands, transit, bus stops and stormwater management.
The traveled way comprises the central portion of the thoroughfare (Figure 9.1). It contains the design elements that allow for the movement of vehicles, transit, bicycles and freight. The traveled way is also where vehicles, via on-street parking, interface with the street-side. Many of the conflicts that occur on thoroughfares occur within the traveled way between two or more moving vehicles, moving and parking vehicles, bicyclists and vehicles, and vehicles and pedestrians crossing at midblock locations and intersections.
Fundamental principles of the design of this portion of the thoroughfare include uniform cross-section along the length of the thoroughfare and transitions designed to move vehicles laterally or change speed where cross-section elements change.
Figure 9.1 The traveled way is the component of the thoroughfare between the curbs. Source: Community, Design + Architecture.
This report addresses the following considerations for the thoroughfare traveled way:
This report addresses the following guidelines for the thoroughfare traveled way:
The following design considerations are used to determine the optimum cross section:
1. Determine context zone and identify thoroughfare type based on Tables 4.1 (Context Zone Characteristics), 4.2 (Thoroughfare Type Descriptions), 4.3 (Relationship Between Functional Classification and Thoroughfare Type), 4.4 (Urban Thoroughfare Characteristics), 6.4 (Design Parameters for Walkable Urban Thoroughfares) and 8.1 (Recommended Streetside Zone Dimensions). This establishes the general parameters for the cross-section (such as median width, parking lane width, streetside width and function).
2. Determine the preliminary number of lanes through a combination of community objectives, thoroughfare type, long-range transportation plans and corridor-wide and network capacity analysis. Network capacity (the ability of parallel routes to accommodate travel demand) should influence the number of lanes on the thoroughfare. Thoroughfare in compact mixed-use urban areas are recommended to have a maximum of six through lanes where necessary because network connectivity is limited. A maximum of four lanes is recommended for new corridors.
3. Select the design and control vehicle for the thoroughfare by identifying the most common type of vehicle to accommodate without encroachment into opposing travel lanes. Chapter 7 describes the selection of a design and/or control vehicle and criteria for accepting encroachment of vehicles into opposing lanes.
4. Determine the preliminary number of turn lanes at critical intersections. Intersection design in CSS may require evaluation of trade-offs between vehicular capacity, level of service, pedestrian crossing distance and exposure to traffic.
5. Identify transit, freight and bicycle requirements for the thoroughfare and establish the appropriate widths for each design element.
6. Develop the most appropriate cross-section and compare the width to the available right of way:
Avoid combining minimal widths for adjacent elements, except on very low-speed facilities (25 mph maximum). For example, avoid combining minimal parking and bicycle lanes adjacent to minimum width travel lanes. Establish priorities for each mode and allocate the right-of-way width appropriately to that mode's design element. Use appropriate lane widths to accommodate the speed and design vehicle selected for the thoroughfare. Avoid maximum-width travel lanes if not warranted, as this creates overly wide thoroughfares that encourage high speeds.
Access management is the practice of properly locating and designing access to adjoining properties to reduce conflicts and improve safety while maintaining reasonable property access and traffic flow on the public street system. Effective access management includes setting access policies for streets and abutting development, linking designs to these policies, having the access policies incorporated into legislation and having the legislation upheld in the courts.
Access management addresses the basic questions of when, where and how access should be provided or denied and what legal or institutional provisions are needed to enforce these decisions. It has been shown that good access management can reduce crashes by 50 percent or more, depending on the condition and treatment used (TRB 2003). The need for rigorous access management in compact urban areas can be lessened by proper network planning, because traffic distributed to a grid of streets reduces the concentration on any one thoroughfare.
The following principles define access management techniques:
There are a number of resources listed at the end of this chapter that provide detailed guidance on access management.
Emergency Vehicle Operations
Urban thoroughfares are the primary conduits for emergency response vehicles, including police, fire and ambulance. Common design for thoroughfares encourages speed and capacity. This can lead to fatality- and injury-producing crashes. On the other hand, the emergency responder bears the responsibility for both response times and reasonable access to incidents within the community. A balance between these two interests must be established for the appropriate design of context sensitive thoroughfares. Both interests can work together to find response strategies that create safe and comfortable places for the non-motorist.
Emergency vehicle access and operations should always be considered in thoroughfare and site design. Local operational conditions will vary from place to place, and emergency response strategies are specific to the locale. Consequently, the practitioner should collaborate with emergency responders to learn their specific needs and response strategies and tactics used on similar streets. Asking the following questions will help in understanding issues when working with fire departments:
Fire codes may have additional guidance on emergency access requirements, such as minimum travel way clear widths and minimum space to deploy certain types of equipment, such as ladders, to reach high buildings. The following should be considered in designing networks and traveled ways to accommodate emergency vehicles:
Operational and technological strategies to enhance emergency vehicle response in urbanized areas include:
1. Reducing nonrecurring congestion using techniques such as traffic incident management and information, special events traffic management, work zone management and emergency management planning; and
2. Reducing recurring congestion using techniques such as freeway and arterial management, corridor traffic management and travel demand management. These include techniques to improve day-to-day operations such as signal systems management, emergency vehicle preemption, access management, traveler information and intelligent transportation systems (ITS), which encompass many of the strategies listed in item 1 above.
Finally, it should be noted that firefighters are trained in many techniques that address context sensitive streets, mainly because narrow, low-speed, pedestrian oriented streets exist in many towns and cities. Many fire departments have experience with historic networks of narrow streets. Their experience provides a basis for allowing new neighborhoods to be built on networks of relatively narrow streets. The designer should be particularly sensitive to the local fire official's experience and operational needs on urban thoroughfares.
Figure 9.2 A mountable median allows emergency vehicles to access side streets. Source: Kimley-Horn and Associates, Inc.
Transitions refer to a change in thoroughfare type, context (rural to urban), right-of-way width, number of lanes, or neighborhood or district. For purposes of this report, transitions in the geometric design of thoroughfares refer to the provision of a smooth taper of appropriate length where lanes or shoulders change width, lanes diverge or merge, or lanes have been added or dropped.
In context sensitive thoroughfare design, however, transitions extend beyond geometric design requirements and reflect changes in context zone and associated levels of multimodal activity. As such, transitions can serve as a visual, operational and environmental cue of the following upcoming changes in:
Principles for designing effective transitions include
If the purpose of the transition is to signal a change in context, neighborhood or district and/or change in speed zone, the transition principles include:
1. Providing a transition speed zone. The purpose of a transition speed zone is to avoid large reductions in the speed limit by providing two or more speed limit reductions. At a minimum, speed-reduction zones use regulatory speed limit signs. Speed limit reductions should occur on tangent sections distant from intersections. Changes in speed zones can utilize other traffic control devices such as warning signs, beacons and so forth as appropriate or can utilize appropriate traffic calming devices such as speed platforms or rumble strips where the zone is particularly short.
2. Providing visual cues to changes in context or environment. The intent of this principle is to combine regulatory speed change with traveled way or streetside features that influence driver speed. Visual cues can include streetside urban design features (landscaping, curbs, on-street parking, street light standards with banners, entry signs, thematic street furniture and so forth) and alternative pavement texture/material at intersections and crosswalks. Land uses and building style can provide visual cues as well. Progressively introducing taller buildings closer to the street affects driver perception of the change from rural or suburban to urban character. Vertical elements, such as street trees in which the vertical height is equal to or greater than the street width, may influence driver perception of the environment and indicate a change. Visual cues should culminate in a gateway at the boundary of the change in district, neighborhood, or thoroughfare. Gateways (Figure 9.3) can be achieved with urban design features or unique intersections such as modern roundabouts.
3. Changing the overall curb to curb width of the street as appropriate for the context, thoroughfare type and traffic characteristics. This can apply to transitions where streets narrow from four to two lanes or widen from two to four lanes. Means of reducing overall street and traveled way pavement width include reducing the number of lanes, reducing lane widths, dropping through lanes as turning lanes at intersections, providing on-street parking or bicycle lanes, applying curb extensions at intersections and midblock crossings and providing a raised curbed median.
Design guidance for the traveled way elements of the thoroughfare are provided in the following sections.
Lane Width Background and Purpose
Street width is necessary to support desirable design elements in appropriate contexts, such as to provide adequate space for safe lateral positioning of vehicles, on-street parking, landscaped medians and bicycle lanes. Wide streets (greater than 60 feet), however, create barriers for pedestrians and encourage higher vehicular speeds. Wide streets can reduce the level of pedestrian interchange that supports economic and community activity. Wide streets discourage crossings for transit connections. The overall width of the street affects the building height to width ratio, a vertical spatial definition that is an important visual design component of urban thoroughfares. Lane width is only one component of the overall width of the street but is often cited as the design element that most adversely affects pedestrian crossings. In fact, many factors affect pedestrian crossing safety and exposure, including the number of lanes, presence of pedestrian refuges, curb extensions, walking speed and conflicting traffic movements at intersections.
Figure 9.3 An arterial gateway into a downtown area composed of a raised intersection, public art, building orientation and attractive materials. Source: Kimley-Horn and Associates, Inc.
General Principles and Considerations
General principles and considerations in the selection of lane widths include the following considerations.
Related Thoroughfare Design Elements
Select lane widths based on the following four key considerations:
AASHTO highlights benefits of narrower (10 to 11 feet) travel lanes on lower-speed urban streets, including a reduction in pedestrian crossing distance, ability to provide more lanes in constrained rights of way and lower construction cost. The recommended travel lane widths in this report are also consistent with design guidelines in AASHTO's Guide for Development ofBicycle Facilities (1999) and the recommendations in A Guide for Achieving Flexibility in Highway Design (2004b).
Research on the relationship between lane width and traffic crashes found no statistically significant relationship between lane width and crash rate on arterial streets (TRB 1986).
Figure 9.4 Bike lanes on the Embarcadero in San Francisco. This multimodal boulevard along the waterfront was formerly an elevated freeway. Source: Dan Burden, walklive.org.
Background and Purpose
Medians are the center portion of a street that separates opposing directions of travel. Medians vary in width and purpose and can be raised with curbs or painted and flush with the pavement. Medians on low-speed urban thoroughfares are used for access management, accommodation of turning traffic, safety, pedestrian refuge, landscaping and lighting and utilities. Based on these functions, this guidance addresses raised curbed medians with a discussion of alternate applications such as flush medians interspersed with landscaped median islands.
In addition to their operational and safety functions, well-designed and landscaped medians can serve as a focal point of the street or an identifiable gateway into a community, neighborhood, or district. Medians can be used to create tree canopies over travel lanes, offer attractive landscaping and provide space for lighting and urban design features. Wider medians can provide pedestrian refuge at long intersection crossings and midblock crossings. Medians vary in width depending on available right of way and function. Because medians increase the width of a street, the designer must weigh the benefits of a median against the increase in pedestrian crossing distance and possible decrease in available streetside widths.
Operational and safety benefits of medians include storage for turning vehicles, enforcing turn restrictions, reducing conflicts, pedestrian refuge, snow storage, reducing certain types of crashes such as head-on collisions and space for vehicles crossing the thoroughfare at unsignalized intersections. With some innovation in design, curbed medians can provide biofiltration swales to retain and improve the quality of stormwater runoff.
Flexibility in median width design revolves around the median's function, appurtenances and landscaping to be accommodated in the median and available right of way. The designer needs to consider the trade-offs between the provision of a median and other design elements, particularly in constrained rights of way.
Related Thoroughfare Design Elements
General Principles and Considerations
General principles and design considerations regarding medians include the following:
Median width may vary to accommodate a pedestrian refuge and/or turn lane. For example, designers may remove on-street parking near intersections in order to laterally shift the travel lanes to accommodate a median with a turn pocket. Where right of way is available, a continuous dimension for the median is preferred.
In constrained rights of way, consider narrower medians with attractive hardscape and urban design features in lieu of planting, or provide a discontinuous median as right of way permits.
Where flush medians are desirable to maintain access to fronting property (e.g., suburban commercial corridors), consider using textured or colored paving or stamped concrete for the median lane interspersed with raised landscaped islands to channelize turning traffic, divide opposing lanes of traffic and provide pedestrian refuge where appropriate (such as midblock and intersection crossings).
Landscaping on medians should be designed in a manner that does not obstruct sight-distance triangles.
Table 9.1 presents the recommended practice for median widths for various functions within low-speed thoroughfares (35 mph or less). The recommendations assume arterial and collector streets in urban contexts (C-3 to C-6) with operating speeds of 35 mph or less. Most of the guidance in this report is not applicable to flush or depressed medians or to raised medians with mountable curbs. Note that median widths are measured from face of curb to face of curb.
Additional guidelines regarding medians also include the following:
Trees and Landscaping in Medians
In urban areas, the community may find it desirable to plant trees in raised curbed medians for aesthetic purposes. In general, the guidance in this report is consistent with AASHTO in regards to low-speed urban thoroughfares. Additional information and miti-gative strategies on trees within the public right of way may be found in A Guide for Addressing Collisions with Trees in Hazardous Locations (TRB 2003). General guidelines for median trees include the following:
Figure 9.5 Narrow medians, such as on this boulevard in Chicago, should only be used to restrict turning movements, separate opposing traffic and create space for traffic control devices. Source: The Congress for the New Urbanism.
Figure 9.6 Median nose extended beyond the crosswalk to provide an enclosed pedestrian refuge. Source: Kimley-Horn and Associates, Inc.
Table 9.1 Recommended Median Widths on Low Speed Walkable Thoroughfares (35 mph or less)
|Thoroughfare Type||Minimum Width||Recommended Width|
|Median for access control|
|All thoroughfare types||4 feet||6 feet1|
|Median for pedestrian refuge|
|All thoroughfare types||6 feet||8 feet|
|Median for street trees and lighting|
|All thoroughfare types||6 feet2||10 feet3|
|Median for single left-turn lane|
|Collector avenues and streets||10 feet4||14 feet|
|Arterial boulevards and avenues||12 feet||16-18 feet|
|Median for dual left-turn lane|
|Arterial boulevards and avenues||20 feet||22 feet|
|Median for transitway|
|Dedicated rail or transit lanes||22 feet||22-24 feet|
|Added median width for platforms||10 feet for each side platform 30 feet for center platform|
1 A 6-foot-wide median is the minimum width for providing a pedestrian refuge.
2 Six feet (measured between curb faces) is generally considered a minimum width for proper growth of small trees less than 4 inches in diameter at maturity. A 10-foot median is recommended for larger trees.
3 Wider medians to provide generous landscaping are acceptable, if desired by the community. However, avoid designing medians wider than necessary to support its desired function at intersections. This can reduce the operational efficiency of the intersections and invite undesirable behavior of crossing traffic such as side-by-side queues, angled stopping and so forth.
4 A 10-foot wide median allows for a striped left-turn lane (9 to 10 feet wide) without a median nose.
Figure 9.7 Maintain a minimum 18-inch offset between the face of median tree (at maturity) and the face of curb. Source: Dan Burden, walklive.org.
Example Landscape Setbacks from Utilities
Overhead electric—10, 15, or 20 feet, depending on tree height
Sanitary sewer main—15 feet all tree species
Water main—10, 15, or 20 feet, depending on tree size
Fire hydrant—5 feet all landscaping, 10 feet all trees
Water meter—5 feet all landscaping, 10 feet all trees
Gas lines—5, 10, or 15 feet, depending on tree size
Underground electric—5, 10, or 15 feet, depending on tree size
Street lights—10 feet all trees
Electric transformers—10 feet front access, 5 feet other sides—all landscaping
Switch cabinet—10 feet front and back access, 5 feet other sides.
Source: Gainesville, FL, Regional Utilities Vegetation Management Tree Planting Guidelines
Landscaping and trees in medians are strongly encouraged in context sensitive design, not only for aesthetics but also for shade, heat island reduction and storm-water interception. The use of medians for pedestrian refuge is recommended to reduce the pedestrian barriers created by wide urban arterials and to support safe design of midblock crossings. As refuges, medians allow pedestrians to focus on crossing one direction of the street at a time, therefore reducing conflicts and decisions. At intersections, pedestrian refuges assist all pedestrians, especially the elderly, to safely cross streets (Figure 9.8).
Some agencies require the use of crash tested barriers when large trees are planted in narrow medians. Consult with the agency on aesthetic treatment of such barriers.
The same rationale for medians on rural highways and conventional urban streets can be applied to context-based design of urban thoroughfares—to provide traffic safety and operational benefits by separating traffic flows, reducing conflicts and creating space for turning vehicles and utilities in the center of the street. In the design of walkable urban streets, the use of medians for traffic safety and operations remains a primary objective but is expanded to emphasize the median's role as an aesthetic amenity to the street and community and to provide pedestrian refuge on wider street crossings.
Figure 9.8 This boulevard median serves as a pedestrian refuge, a community gateway and area for landscaping. Source: Kimley-Horn and Associates, Inc.
Bicycle Lanes Background and Purpose
Bicycle travel should be served on multimodal streets. Bicyclists vary in their level of skill and confidence, trip purpose and preference for facility types; thus, the mobility needs of bicyclists in urban contexts vary as well. Bicycle facilities should encompass a system of interconnected routes, paths and on-street bicycle lanes that provide for safe and efficient bicycle travel. This report focuses only on the provision of bicycle lanes on major thoroughfares— streets that are designated as arterials or collectors. Refer to AASHTO's Guide for the Development of Bicycle Facilities for planning and design guidance for other types of bicycle facilities.
Not all urban thoroughfares will include bicycle lanes. However, except for freeways and streets where bicycling is specifically prohibited, bicyclists are permitted to use any street for travel, even if bicycle lanes are not provided. The design of bicycle lanes on major urban thoroughfares is typically coordinated with a community's or region's master bicycle plan to ensure overall connectivity and the selection of the best streets for implementation of bicycle lanes. However, absence of a designation in a bicycle plan does not exclude the practitioner from providing bicycle lanes if the need exists. The width of the street and the speed and volume of adjacent traffic are the most critical factors in providing safe bicycle lanes. If adequate facilities cannot be provided, then the safety of both the bicyclist and driver is compromised. In urban areas the practitioner is faced with two conditions in designing bicycle lanes: adjacent to curb or adjacent to on-street parking (Figure 9.9). This section addresses these conditions.
Related Thoroughfare Design Elements
Figure 9.9 A bike lane adjacent to parallel parking on an avenue. Source: Kimley-Horn and Associates, Inc.
General Principles and Considerations
Implementation of bicycle lanes can meet many community objectives, including accessibility, connectivity between destinations, youth mobility and increased system capacity. General principles and considerations regarding bicycle lanes include the following:
The design of bicycle lanes in urban areas is well documented. Refer to the Manual on Uniform Traffic Control Devices (FHWA 2009) and Guide for the Development of Bicycle Facilities (AASHTO 1999). For alternative ways to accommodate bicyclists refer to Innovative Bicycle Treatments (ITE 2002).
Figure 9.10 Reverse (back-in) angled parking improves driver visibility of bicyclists. Source: Dan Burden, walklive.org.
Table 9.2 Recommended Practice for Bicycle Lanes on Walkable Urban Thoroughfares
|Minimum Width||Recommended Width|
|Bicycle lane width—combined with on-street parking lane|
|All thoroughfare types||13 feet||13 feet|
|Bicycle lane width—no on-street parking|
|All thoroughfare types||5 feet1||6 feet|
1 Requires a minimum 3-foot ridable surface outside of gutter pan. If no gutter pan is present, the minimum width is 5 feet. Bicycle routes without marked lanes are acceptable for low-volume thoroughfares with target speeds of 25 mph or less.
Table 9.2 presents the recommended practice for bicycle facilities on thoroughfares. The recommendations assume arterial and collector streets in urban contexts with target speeds of 35 mph or less.
Urban thoroughfares within the bicycle network should provide bicycle lanes, particularly where the width of shared lanes is prohibitive or undesirable. The type and experience level of bicycle riders and the volume of bicyclists is a consideration in determining the need for bicycle lanes. Where bicycle lanes are needed and right of way is constrained, the designer needs to understand the trade-offs between adding bicycle lanes and eliminating or reducing the width of other thoroughfare design elements.
On-Street Parking Configuration and Width
Background and Purpose
The presence and availability of on-street parking serves several critical needs on urban thoroughfares: to meet parking needs of adjacent uses, protect pedestrians from moving traffic and increase activity on the street. Usually, on-street parking cannot by itself meet all of the parking demand created by adjacent land uses and typically will supplement the off-street parking supply. On-street parking provides the following benefits:
Related Thoroughfare Design Elements
While this report supports on-street parking as an inherent element of walkable, compact, mixed-use urban areas and a component of the economic health of urban businesses, the practitioner designing walk-able streets should always consider the trade-offs of integrating on-street parking. These include:
On-street parking can result in a 3 to 30 percent decrease in the capacity of the adjacent travel lane, depending on the number of lanes and frequency of parking maneuvers. The designer needs to balance traffic capacity and local access needs when deciding where and when to permit on-street parking. There are methods for minimizing the impact of parking maneuvers on traffic flow. For example, see MUTCD (Figure 3B—17, referenced in Section 3B.18) showing a parallel parking configuration that allows vehicles to drive forward into the parking space.
General Principles and Considerations
General principles and considerations regarding on-street parking include the following:
The preferred width of a parallel on-street parking lane is 8 feet wide on commercial thoroughfares (all types) or where there is an anticipated high turnover of parking and 7 feet wide on residential thoroughfares. These dimensions are inclusive of the gutter pan and applicable to all context zones (C-3 through C-6).
Figure 9.11 Angled parking on a retail-oriented main street in Hayward, CA. Source: Kimley-Horn and Associates, Inc.
On low-volume, low-speed avenues and streets in commercial main street areas, where sufficient curb-to-curb width is available, angled parking may be appropriate. Angled parking should have the dimensions shown in Table 9.3 for a variety of different angles. Head-in angled parking can create sight distance problems associated with vehicles backing out of parking spaces. The use of reverse (back-in) angled parking can be used to overcome sight distance concerns and is considered safer for bicyclists traveling adjacent to angled parking (Figure 9.12).
Table 9.3 Minimum Dimensions for Head-In Angled On-Street Parking*
|Angle||Stall Width||Stall Depth (Perpendicular to Curb)||Min. Width of Adjacent Lane||Curb Overhang|
|45°||8.5-9.0 feet||17 feet 8 inches||12 feet 8 inches||1 foot 9 inches|
|50°||8.5-9.0 feet||18 feet 3 inches||13 feet 3 inches||1 foot 11 inches|
|55°||8.5-9.0 feet||18 feet 8 inches||13 feet 8 inches||2 feet 1 inches|
|60°||8.5-9.0 feet||19 feet 0 inches||14 feet 6 inches||2 feet 2 inches|
|65°||8.5-9.0 feet||19 feet 2 inches||15 feet 5 inches||2 feet 3 inches|
|70°||8.5-9.0 feet||19 feet 3 inches||16 feet 6 inches||2 feet 4 inches|
|90°||8.5-9.0 feet||18 feet 0 inches||24 feet 0 inches||2 feet 6 inches|
Source: Dimensions of Parking, 4th Edition, Urban Land Institute Notes:
Typical design vehicle dimensions: 6 feet 7 inches by 17 feet 0 inches. Use 9.0 feet wide stall in commercial areas with moderate to high parking turnover. *For back-in angled parking, reduce curb overhang by one foot.
Figure 9.12 Reverse (back-in) angled parking improves driver visibility. Source: Dan Burden, walklive.org.
Additional guidelines regarding on-street parking include the following:
The recommendations in this report are based on the principles presented in the AASHTO Green Book and pedestrian facilities guide. The Green Book states that the "designer should consider on-street parking so that the proposed street or highway improvement will be compatible with the land use ... the type of on-street parking should depend on the specific function and width of the street, the adjacent land use, traffic volume, as well as existing and anticipated traffic operations."
Geometric Transition Design Background and Purpose
Transitions refer to a change in the width or speed of a thoroughfare or the need to laterally shift vehicles. In terms of geometric design, transitions refer to the provision of an adequate taper where lanes shift or narrow, shoulders widen, lanes diverge or merge and where deceleration lanes are provided. Geometric transitions are usually required when there is a change in the thoroughfare type and associated change in width, particularly where functional classification and speed changes and where a change in the width of roadway, either a narrowing or widening of lanes, or a decrease or increase in number of lanes is introduced. Refer to the section transition principles earlier in this chapter for guidance on nongeometric transitions.
For changes in roadway width and space designing a geometric transition such as a lateral shift, lane addition or drop, lane or shoulder narrowing and so forth, use the established guidance in the MUTCD, where the length of the transition taper is computed by the following equation:
Figure 9.13 Typical transition design and markings. Source: Community, Design + Architecture, adapted from the Manual on Uniform Traffic Control Devices (FHWA).
(Extended text description: Diagram depicts typical transition design and markings with title text that reads Lane Reduction Markings. There are three smaller diagrams contained in the full diagram. Illustration A contains from 3 lanes to 2 lanes, showing the signage and an area of L length where 3 lanes reduce to 2 lanes, and variables W and d leading up to the lane reduction. Illustration B shows from 4 lanes to 3 lanes and also indicates length L where 4 lanes reduce to 3 lanes. Illustration 3 shows from 4 lanes to 2 lanes with L length of where the lanes reduce. At the bottom of the larger diagram is a legend which reads L = Length in feet. S = Posted, 85th percentile or statutory speed in mph, W = Offset in feet and d = Advance warning distance. The legend also says, For speeds 45 mph or more L=WS. For speeds under 45mph: L=WS^2/60.)
Four-Lane to Three-Lane Conversions (Road Diets)
A road diet is the conversion of a wide street to a narrower one, such as the conversion of a four-lane undivided thoroughfare into a three-lane street composed of two travel lanes and a two-way left-turn lane. This conversion provides additional space to accommodate other desirable features such as bike lanes, wider street-sides, pedestrian refuge, landscaping, or on-street parking. Case studies demonstrate that road diets reduce conflicts at intersections, reduce accidents and have minimal effects on traffic capacity and diversion on thoroughfares under 20,000 vehicles per day.
Three-lane roadways can improve emergency response by allowing emergency vehicles to bypass congestion by using the two-way left-turn lane. They create opportunities for pedestrian refuges at midblock and intersection crossings and eliminate the common "multiple threat" hazards pedestrians experience crossing four-lane roads. Other benefits include easier egress from driveways (improved sight distance), smaller curb return radius by increasing the effective radius of the road, improvements for transit (allows curbside stops outside of travel lane) and buffers street tree branches from closely passing trucks. Road diets can improve the flow of traffic and reduce travel speeds, particularly when used in conjunction with roundabouts (see Chapter 10 section on modern roundabouts). Figure 9.14 shows a street before and after a road diet.
Converting four-lane roads to three lanes and adding a raised median and on-street parking may result in the thoroughfare failing to meet local fire districts minimum clear travelway requirements. See discussion on emergency vehicle operations earlier in this chapter.
For more detailed information, design guidance and case studies, refer to Road Diet Handbook: Setting Trends for Livable Streets, Second Edition (Parsons Brinkerhoff, Rosales, 2007).
Midblock Crossings Background and Purpose
Midblock crossings provide convenient locations for pedestrians to cross urban thoroughfares in areas with infrequent intersection crossings or where the nearest intersection crossing creates substantial out-of-direction travel. When the spacing of intersection crossings is far apart or when the pedestrian destination is directly across the street, pedestrians will cross where necessary to get to their destination directly and conveniently, exposing themselves to traffic where drivers might not expect them. Midblock crossings, therefore, respond to pedestrian behavior. Properly designed and visible mid-block crosswalks, signals and warning signs warn drivers of potential pedestrians, protect crossing pedestrians and encourage walking in high-activity areas.
Related Thoroughfare Design Elements
General Principles and Considerations
Installing midblock crosswalks can help channel pedestrians to the safest midblock location, provide visual cues to allow approaching motorists to anticipate pedestrian activity and unexpected stopped vehicles and provide pedestrians with reasonable opportunities to cross during heavy traffic periods when there are few natural gaps in the approaching traffic streams (Figure 9.15). General principles and considerations regarding midblock crossings include the following:
Figure 9.14 Before and after illustration of a road diet. Source: Claire Vlach, Bottomley Design & Planning.
The recommended practice for midblock crossings on urban thoroughfares is shown in Table 9.4. Examples are provided in Figures 9.16 through 9.19.
Street life and activity entering and leaving buildings are often oriented toward midblock locations rather than intersections. Pedestrian convenience is related to walking distance as well as safety in crossing the roadway. Well-designed midblock crosswalks are highly visible to motorists, bicyclists and pedestrians; reduce walking distance; and contribute to pedestrian convenience.
Figure 9.15 Midblock crosswalks provide opportunities to cross streets with long distances between intersection crossings. Source: Claire Vlach, Bottomley Design & Planning.
Table 9.4 Recommended Practice for Midblock Crossings
|The decision to locate a midblock crosswalk will be based on numerous factors. Generally, however, consider providing a marked midblock crossing when protected intersection crossings are spaced greater than 400 feet or so that crosswalks are located no greater than 200 to 300 feet apart in high pedestrian volume locations, and meet the criteria below.|
|Midblock crossings may be considered when there is significant pedestrian demand to cross a street between intersections, such as connecting to major generators or transit stops.|
|Midblock crosswalks should be located at least 100 feet from the nearest side street or driveway so that drivers turning onto the major street have a chance to notice pedestrians and properly yield to pedestrians who are crossing the street.|
|Streets with an average daily traffic volume (ADT) of 12,000 vehicles per day or less.|
|Multilane streets carrying less than 15,000 ADT if a raised pedestrian refuge median is provided.|
|Operating speeds less than 40 mph.|
|A minimum pedestrian crossing volume of 25 pedestrians per hour for at least four hours of a typical day.|
|Adequate sight distance is available for pedestrians and motorists.|
|Conform to PROWAG guidelines for the disabled and visually impaired.|
|Unsignalized midblock crosswalks should not be provided on streets where traffic volumes do not have gaps in the traffic stream long enough for a pedestrian to walk to the other side or to a median refuge. At locations with inadequate gaps that also meet MUTCD signalization warrants, consider a signalized midblock crossing.|
|Consider a signalized midblock crosswalk (including locator tone and audio pedestrian signal output as well as visual pedestrian countdown signal heads) where pedestrians must wait more than an average of 60 seconds for an appropriate gap in the traffic stream. When average wait times exceed 60 seconds, pedestrians tend to become impatient and cross during inadequate gaps in traffic. If this initial threshold is met, check pedestrian signal warrants in the MUTCD.|
|Provide overhead safety lighting on the approach sides of both ends of midblock crosswalks.|
|Provide wheelchair ramps or at-grade channels at midblock crosswalks with curbs and medians.|
|Provide raised median pedestrian refuge at midblock crossings where the total crossing width is greater than 60 feet, and on any unsignalized multi-lane thoroughfare crossing.|
|Use high-visibility (ladder-style) crosswalk markings to increase visibility longitudinally.|
|Provide advance stop or yield lines to reduce multiple-threat crashes.|
|Provide advance crosswalk warning signs for vehicle traffic.|
|Provide curb extensions at midblock crosswalks with illumination and signing to increase pedestrian and driver visibility.|
|"Z" crossing configurations should be used for midblock crossings with medians wherever possible (see Figure 9.16). Provide an at-grade channel in median at a 45-degree angle toward advancing traffic to encourage pedestrians to look for oncoming traffic.|
|A strategy to calm traffic speeds in advance of and at a midblock crossing is to raise the pavement to meet the sidewalk elevation by use of gentle ramps (see Figure 9.17). Consider use of overhead flashing beacons.|
Safety Effects of Marked vs. Unmarked Crosswalks at Uncontrolled Locations, FHWA, 2002
Manual on Uniform Traffic Control Devices, FHWA, 2009 Edition
Guide for the Planning, Design and Operation of Pedestrian Facilities, AASHTO, 2004
Figure 9.16 Midblock crossings with a "Z" configuration force pedestrians crossing the median to look toward oncoming traffic. Avoid street trees that interfere with visibility. Source: Kimley-Horn and Associates, Inc.
Figure 9.17 The raised roadway crosswalk concept combines midblock crosswalks with traffic calming devices. Source: Kimley-Horn and Associates, Inc.
Figure 9.18 Midblock crossing with pedestrian detection and in-pavement lights. Source: Kimley-Horn and Associates, Inc.
Figure 9.19 Example of a signalized midblock crossing. Source: Kimley-Horn and Associates, Inc.
Figure 9.20 Refuge islands can be used at midblock locations, channelized right turns, or at long intersection crossings. Source: Kimley-Horn and Associates, Inc.
Pedestrian Refuge Islands Background and Purpose
Refuge islands provide pedestrians and bicyclists a refuge area within intersection and midblock crossings. While in walkable urban areas it is desirable that thoroughfares have short crossings, on wide thoroughfares, or where less mobile pedestrians need to cross, refuge islands provide a location for pedestrians or bicyclists to wait partially through their crossing. Refuge islands also break up crosswalks at complex multilane and multilegged intersections into shorter and easier portions for pedestrians to cross.
Related Thoroughfare Design Elements
Refuge islands are provided in the median and on right-turn channelized islands (Figure 9.20). Refuge islands should be considered for intersections and mid-block crossings for which one or more of the following conditions apply: • Unsignalized midblock and intersection crossings of a high-volume thoroughfare of four or more lanes to allow crossing pedestrians and bicyclists to concentrate on crossing one direction of travel at a time; or
At signalized intersections, the provision of pedestrian refuges increases the crossing distance of most pedestrians (walking at a rate of 3.5 to 4 feet per second) who do not need to use the refuge and increases the traffic signal's overall cycle length and resulting delay (delay that is also experienced by pedestrians). Thus, the practitioner needs to balance the needs of all users when considering a refuge in the second condition above.
Recommended practices regarding pedestrian refuge islands include the following:
Short crosswalks help pedestrians cross streets more safely with less exposure to vehicle traffic. They also require shorter pedestrian signal phases to cross, thereby reducing traffic delays. Pedestrian comfort and safety when crossing wide intersections is an essential component of good pedestrian facility design. On wide streets, the median can provide a refuge for those who begin crossing too late or are slow walkers. At unsignalized intersection and midblock crossings, medians permit crossings to be accomplished in two stages, so that pedestrians only have to concentrate on crossing one direction of the roadway at a time.
Transit Design Background and Purpose
Many urban thoroughfares accommodate public transportation. The types of services accommodated on thoroughfares ranges from local bus service to bus rapid transit (BRT) to trolleys and light rail transit (LRT). These types of transit service can be accommodated either within a dedicated right of way in the thoroughfare or in mixed-flow lanes. In both cases the design of the thoroughfare needs to consider the special requirements of transit vehicles, running ways and operations, whether they exist or are planned for the future. The purpose of this section is to identify the key elements of transit that affect the design of thoroughfares. Detailed design guidance on dedicated transitways, particularly for rail systems, is beyond the scope of this report, but the information presented here can inform the thoroughfare planning and design process.
Related Thoroughfare Design Elements
Table 9.5 Types of Public Transportation Using Urban Thoroughfares
|Local Bus||Bus service operating at a fixed frequency that serves designated stops along a fixed route. Fares are collected onboard by the bus operator. Local bus service usually operates in mixed-flow lanes on urban thoroughfares. The typical average operating speed is low and is dependent on the operating speed of the urban thoroughfare.|
|Rapid Bus||Bus service similar to local bus serves designated stops along fixed route but with fewer stops than local service. This service is also known as commuter express. Fares are collected onboard by the bus operator. Rapid bus service usually operates along mixed-flow lanes on urban thoroughfares. Rapid buses may operate only during peak travel periods along peak directions. Some rapid bus systems use transit priority signal systems to improve headways, and queue jump lanes to bypass congestion at intersections.|
|Bus Rapid Transit (BRT)||Enhanced bus service that operates within its own right of way or designated lanes along the urban thoroughfares. BRT may utilize off-board fare collection to minimize boarding delays. BRT stops are typically spaced one mile apart and operate with high-frequency headways. The average speed of BRT is higher than that of rapid bus. BRT buses and stations are branded to distinguish them from local bus services. Stations frequently have more passenger amenities than typical bus stops. BRT systems use transit priority signal systems to improve headways, and queue jump lanes to bypass congestion at intersections.|
|Streetcar/Light Rail Transit (LRT)||Streetcars and LRT are fixed guideway transit systems. Streetcars (or trolleys) are electrically powered vehicles that may share the street with other modes of transportation and operate in mixed-flow lanes. LRT is typically electrical powered rail cars within exclusive rights of way in thoroughfare medians but may also operate in mixed-flow lanes. LRT is provided with traffic signal prioritization at intersections and requires special signal phasing to reduce conflicts. LRT utilizes off-board fare collection at transit stations. Transit stations, whether on the median or edges of thoroughfares, may require substantial right of way.|
Figure 9.21 An example of a dedicated transitway in the outside lane of an urban thoroughfare. Note the bike lane located between the curb and the transitway. Source: Kimley-Horn and Associates, Inc.
Types of Transit on Thoroughfares
The different types of public transportation systems that use urban thoroughfares have varying physical and operating characteristics that will establish the design controls and geometric design parameters in thoroughfare design. It is important for the practitioner to understand the dimensions and capabilities of the type of transit using, or expecting to use, the thoroughfare and the ramifications the transit vehicles, their operation and their stops and stations will have on the design of the thoroughfare.
Table 9.5 describes the common types of public transportation systems using urban thoroughfares.
Transit Facilities on Thoroughfares
Transit on urban thoroughfares can utilize one or more of the following running way configurations:
Each running way configuration requires that the practitioner understand the right of way and dimensions required (not only for the running ways but for stops and stations), the transition required when changing from one configuration to another and how the transit vehicle will use intersections. Further, rail systems can be single tracked, double tracked, or both, which affects thoroughfare width planning.
Like running ways, bus and rail stops and stations can have multiple configurations depending on the type of transit, the available right of way, the type of service and other factors. As used in this report, a "stop" is a location where a transit vehicles stops to allow passengers to board or alight. A stop, at a minimum, is identified by a sign but may have some passenger amenities such as benches and shelters. A "station" is a more elaborate transit stop with substantial passenger amenities and may have facilities such as ticket offices, restrooms, or other services. Stations may accommodate multiple vehicles or have integrated in-termodal facilities. Stops and stations can utilize one or more of the following configurations:
Local, Rapid and Bus Rapid Transit
Light Rail, Streetcar, or Trolley Transit
Figure 9.22 A simulation of a bus rapid transit center median station with dual outside platforms located at the far side of an intersection. Source: AC Transit.
Figure 9.23 This thoroughfare in Houston, Texas has light rail transit running in dedicated inside travel lanes. Source: Texas Transportation Institute.
Table 9.6 Integrating Transit into Thoroughfare Planning and Project Development
|Thoroughfare Planning or Project Development Stage||Transit Considerations|
Systems and Network Planning
Identify thoroughfare network deficiencies and conceptual solutions
|Identify transit system deficiencies and long range transit needs|
Develop and assess alternatives for corridor
|Develop and assess thoroughfare and transit alternatives within the corridor|
Develop project definitions that address deficiencies
|Identify transit elements to be included in the definition of thoroughfare projects|
Prioritize projects and define program based on funding availability
|Develop transit project phasing and identify transit elements to be included in project funding|
Environmental and Design
Design project, assess impacts and estimate cost
|Identify transit requirements to be integrated into thoroughfare design|
Adapted from Transit Vehicles and Facilities on Streets and Highways (Phase II) Final Report. Transit Cooperative Research Program Project D-09, 2007. Privileged Document.
The thoroughfare designer needs to coordinate with the responsible transit agencies to identify the appropriate running way configuration, transitions and location and design of stops and stations.
Planning for Transit
Transit systems are planned at the regional, citywide and/ or corridor level (see Chapter 2). Most large-scale rail transit system decisions (technology, type, service and routing) are made in statewide or regional long-range transportation plans. Typically, an alternatives analysis that evaluates the feasibility of implementing the transit system on the proposed routes is prepared for major public transportation systems such as LRT or BRT that seek federal funding. These studies may even include preliminary engineering. Transit systems planning and corridor planning follow the same general process outlined in Chapter 2 for the thoroughfare planning process.
Transit considerations can be integrated into thoroughfare planning and design at several stages within the regional planning, corridor planning and project development processes as outlined in table 9.6.
When designing thoroughfares that are identified as future transit corridors, the practitioner will need to consider a number of factors in order to reserve the appropriate right of way and to ensure the design is relatively easily converted to accommodate transit. Some of these factors are identified in table 9.7. In addition to specific design issues, the practitioner may need to consider other planning considerations such as:
Transit Design Parameters
Although it is not the intent of this report to present guidelines for the extensive field of transit facility design, table 9.8 presents a select number of minimum dimensions and design parameters for some of the more common transit facility components that might be useful to the thoroughfare design practitioner in determining cross-sectional elements.
Table 9.7 Transit Related Factors to Consider in Thoroughfare Design
|Thoroughfare Design Component||Factors to be Considered|
|Streetside (Chapter 8)||Streetside width at stops or stations|
|Space for passenger requirements such as shelters, seating, waiting areas, trees, lighting and so forth.|
|Accessibility requirements (lift pads)|
|Traveled Way (Chapter 9)||Available total right of way to accommodate running ways, stops and stations|
|Lane width to accommodate transit vehicle in mixed-flow lanes|
|Type of running way and separation (dedicated transitway, reversible/contraflow, HOV, median lanes, concurrent lanes)|
|Median width to accommodate running ways and stations|
|Pedestrian access to median stations|
|Ability to accommodate on-street parking on transit streets|
|Parking restrictions near stops and stations|
|Bike/bus conflicts where buses stop in bike lane|
|Pavement depth to accommodate buses; concrete pads at bus stops|
|Additional width for transit facilities versus pedestrian crossing distance|
|Roadway structural design for LRT|
|Horizontal and vertical clearances for transit; maintenance requirements such as tree pruning|
|Necessity for bus bays|
|Transit operations on one-way streets, location of stops, turns|
|Provision of an enforcement area on exclusive bus facilities (e.g., extended bus turnouts)|
|Prohibition of turns across median running ways|
|Overhead clearance for catenary power supply or trolley wires and space to mount poles|
|Intersections (Chapter 10)||Transit vehicle turning radius and curb return/extension design|
|Queue jump lanes and special signal phasing|
|Accommodating transit vehicles in roundabouts|
|Near-side or far-side bus stops, BRT or rail stations and traffic operations|
|Transit priority signal systems or special phasing for rapid and BRT|
|Bus priority treatments; intersection design when contraflow bus lanes are used|
|Special signal phasing and equipment for LRT|
|Vehicle left-turn lanes adjacent to median stations|
|Vehicle turn prohibitions in constrained rights of way or for operational efficiency|
|Curb extension bus stop versus curbside stop|
|Pavement grades through intersections and bus passenger comfort|
|Movement restrictions and bus exemptions|
Table 9.8 Minimum Dimensions for Transit Facilities in Thoroughfares
|Transit Facility or Design Element||Minimum Dimension|
|Lane width to accommodate standard urban bus, LRT vehicle, or streetcar||11 feet|
|Curbside bus stop length and no-parking zone (add 20 feet for articulated vehicles)|
|Near-side bus stop||100 feet|
|Far-side bus stop||
(Plus 5 feet from crosswalk or curb return)
|Far-side bus stop after turn||
(Plus 5 feet from crosswalk or curb return)
|Bus bulb stop length (near side or far side)||40 feet|
|Distance between front of vehicle at near-side stop and crosswalk||10 feet|
|Single-side LRT/BRT platform width conforming to ADA guidelines||
(8 feet plus 2 feet tactile strip)
|Distance between LRT double track centerlines||12 feet|
|Maximum grade for LRT operation||6%|
|Height of platform||Low: 10 inches High: 36 inches|
|Width of two-track LRT channel||22 feet|
|Vertical clearance for LRT (top of rail to bottom of wire)||11.5 feet|
|Width of right of reserve for two tracks||19-33 feet|
|LRT/BRT station widths (including running way)|
|Dual outside platforms||41 feet|
|Single center platform||55 feet|
|Single outside platform||31 feet|
Bus Stops in the Traveled Way Background and Purpose
There are more than 9.4 billion trips made by transit in the United States each year, with nearly 5.3 billion trips made by bus (National Transit Database 2006). Buses are the most common form of mass transit in the country, and the majority of bus travel occurs on urban thoroughfares in metropolitan areas. Since urban thoroughfares serve as the primary access and mobility routes for mass transit, they are the best locations for investment in transit facilities and public amenities that provide direct access to bus stops and functional, attractive and comfortable places to wait for transit. The placement and design of bus stops affect the efficiency of the transit system, traffic operations, safety and people's choices to use transit. Since there is no equivalent to the AASHTO Green Book for transit design guidance, transit agencies develop guidelines and practices for bus stop planning, placement and design. Design guidelines include compliance with ADA requirements to ensure that transit is accessible. This section addresses general guidance for the planning and design of bus stops on urban thoroughfares compiled from the design guidelines of transit agencies. Location-specific guidance should be obtained from local transit agencies.
Related Thoroughfare Design Elements
General Principles and Considerations
Fundamentals of Bus Stop Placement
The location of a bus stop must address both traffic operations and passenger accessibility issues. If possible, the bus stop should be located in an area where typical amenities, such as a bench or shelter, can be placed in the public right of way. A bus stop location should consider potential ridership, traffic and rider safety and bus operations elements that require site-specific evaluation. Significant emphasis should be placed on factors affecting personal security. Well-lit open spaces visible from the street create a safer environment for waiting passengers.
Elements to consider when determining bus stop placement include:
Traffic and rider safety elements to consider in bus stop placement include:
Bus operations elements to consider in bus stop placement include:
Table 9.9 Advantages and Disadvantages of Midblock Bus Stops
The preferred location for bus stops is the near side or far side of an intersection (see the section on intersection bus stops in Chapter 10). Intersection stops provide the best pedestrian accessibility from both sides of the street and the cross streets and provides connection to intersecting bus routes.
Bus stops may also be placed at a midblock location on long blocks or to serve a major transit generator. At midblock bus stops ensure crosswalks are placed behind the bus stop, so passengers do not cross in front of the bus, where they are hidden from passing traffic. table 9.9 presents the advantages and disadvantages of midblock bus stops.
Stops should be placed to minimize the difficulties associated with lane changes and weaving maneuvers of approaching vehicles. Where it is not acceptable to stop the bus in traffic and a bus pullout is justified, a far-side or midblock curbside stop is generally preferred (see section on intersection bus stops in Chapter 10).
Standard transit bus dimensions
Overall height: 10 feet, 6 inches
Overall width: 10 feet, 4 inches (including mirrors)
Overall length (large bus): 40 feet
Overall length (articulated bus): 60 feet
Wheelchair lift dimensions
Width: 4 feet
Extension (from edge of bus): 4 feet, 6 inches
Inner rear wheel - 25.5 feet
Outer front corner - 47.8 feet
Centerline radius - 40.8 feet 60-foot articulated:
Inner rear wheel - 21.3 feet
Outer front corner - 44.3 feet
Centerline radius - 35.5 feet
Source: Orange County Transportation Authority (OCTA) Bus Stop Safety and Design Guidelines, Orange County, California
|Minimizes sight distance problems for motorists and pedestrians||Requires additional distance for no-parking restrictions|
|Might result in passenger waiting areas experiencing less pedestrian congestion||Increases walking distance for patrons crossing at an intersection or requires special features to assist pedestrians with midblock crossing|
|Might be closer to passenger origins or destinations on long blocks||Encourages uncontrolled midblock pedestrian crossings|
|Might result in less interference with traffic flow||Only serves adjacent generators and does not afford system transfers to other lines often found at intersections|
Spacing of Bus Stops
Optimal bus stop spacing varies depending upon the type of transit service provided, urban context zone, location of major attractors, physical barriers and local community goals. Appropriate spacing ranges from 400 to 500 feet for downtown circulator shuttles and low-volume community service routes to greater than 2,000 feet (up to one mile) for bus rapid transit and express lines. Designers should consult with the local transit provider for design guidance on bus stop spacing and placement.
On urban thoroughfares with transit routes, the bus is one of the design vehicles used in thoroughfare design. Some transit agencies use smaller, urban-scaled transit vehicles (32-foot coach) and use of vehicles with the smallest possible turning radii should be encouraged. Most fleets use standard coaches with the design specifications described here. Important dimensions of standard and articulated buses are shown in the sidebar, including the turning radii requirements for a 40-foot coach and 60-foot articulated bus. The minimum inside radius is 21 to 26 feet and the minimum outer radius is 44 to 48 feet. Turning templates should be used in the design of facilities to identify curb return radius and required pavement width to avoid vehicle encroachment into opposing travel lanes. Additional allowance should be made for:
Parking Restrictions at Bus Stops
It is important that parking restrictions (either curb markings or NO PARKING signs) be placed at bus zones (Figure 9.24). The lack of parking restrictions impacts bus operations, traffic movement, safe sight distance and passenger access. Considerations include:
Figure 9.24 Parking restrictions at a bus stop. Source: Texas Transportation Institute.
In addition to a minimum 40- to 60-foot long bus stop, no-parking zones before and after the bus stop allow buses to pull into the bus stop and reenter traffic. Use the following dimensions for no- parking zones at midblock bus stops that typically accommodate a single bus:
Parking restrictions are not necessary when curb extension bus stops are provided.
Curb Extension Bus Stops at Midblock Locations
Bus bulbs (or curb extension bus stops) are bus stops in which the curb is extended into the on-street parking lane, and the bus stops within the travel lane. Refer to Chapter 10 (Curb Extension Bus Stops) for more information on this type of stop.
Figure 9.25 A typical bus turnout on an arterial Avenue. Source: Kimley-Horn and Associates, Inc.
Bus turnouts (a recessed curb area located adjacent to the traffic lane as shown in Figure 9.25) are desirable only under selected conditions because of the delay created when the bus must reenter traffic. Bus turnouts are typically used only on thoroughfares with higher target speeds than those included in this report.
Bus turnouts have the following advantages:
Bus turnouts have the following disadvantages:
Bus Turnout Design
Typical urban bus turnouts are usually comprised of an entrance taper (40 to 60 feet), stopping area (40 to 60 feet per each standard and articulated bus respectively) and exit taper (40 to 60 feet).
Passenger Boarding Area
The bus stop passenger boarding area is the area described as a firm, solid platform for deployment of wheelchair lifts and for other bus stop features, such as shelters, and benches. The boarding area must include a front and rear loading area free of obstacles. The boarding area may also be a pathway, but greater clearance than a typical sidewalk is required to allow deployment of the wheelchair lift. Figure 9.26 shows a basic boarding area.
The following criteria for boarding areas should be used to ensure compliance with PROWAG requirements:
Figure 9.26 A simple passenger boarding area. Source: Kimley-Horn and Associates, Inc.
Every bus stop should include the following minimum elements for passenger accessibility, safety and comfort:
Security is one of the primary issues associated with the design of bus stops. Personal security is consistently mentioned in transit studies as a major concern among transit users. The following guidelines should be considered to improve security at bus stops:
Figure 9.27 An example layout of a shelter and other street furniture. Source: Texas Transportation Institute.
Figure 9.28 This bus stop is designed so that stormwater drains away from the curb into a slot drain located in the travel lane. This design keeps buses from splashing waiting passengers when pulling to the curb. Source: Texas Transportation Institute.
Bus stops should be designed to first expedite the safe and efficient loading and unloading of passengers (including those with disabilities) and to allow for efficient transition of the bus between the travel lanes and the bus stop. Because of the multimodal function of urban thoroughfares and to make transit competitive with auto travel, consideration should be given to design features that minimize delay for buses reenter-ing the traffic stream (far-side bus stop placement and curb extension bus stops). The boarding area must be designed, at a minimum, to accommodate ADA/ PROWAG requirements, but consideration should be given to boarding areas that can accommodate passenger amenities such as shelters, benches, trees and bicycle parking, even if these amenities will be implemented in the future.
Special Consideration with Stormwater Management
The management of stormwater on walkable urban thoroughfares improves the walking and bicycling environment, aesthetics and the quality of the community as a whole. Green stormwater management practices add value and multiple functionality and should be considered in thoroughfare improvement projects.
Swales in Stormwater Management
Green swale areas can be located in medians, planting strips, islands and other landscaped areas to which stormwater can be directed. Swales are depressed areas that are normally highly porous but are planted with low-maintenance, frequently indigenous types of grass or vegetation that are compatible with the detention, absorption and filtration functions they are designed to serve. The photos below show an example of a median swale, but similar swales can be located in planting strips adjacent to curbs or other locations within the right of way.
If the local soil doesn't percolate or if the median slopes, the design will need a subsurface drain inlet to the storm drain system at the downstream end (as shown in the photo above). Consider that loose soil around the plants would be carried into the storm drain with the first storm requiring fabric or other erosion control on the soil or a sediment trap in the inlet structure.
Source: City of Gresham, OR
Stormwater runoff from thoroughfares and their streetsides must be handled in the right of way. Different communities treat stormwater differently. For some the conventional way is to collect and carry it in storm sewer pipe networks to a treatment plant then an outfall into a water body. For other communities, stormwater is controlled at the source or through treatment control best management practices.
Related Thoroughfare Design Elements
Background and Purpose
Urban areas have a high percentage of impervious surfaces. This creates the need for stormwater systems that can carry the runoff away from the area or treat, absorb and/ or detain the runoff at its source. Failure to sufficiently handle stormwater can result in increased volume and rate of runoff from impervious surfaces increasing the demand for stormwater system capacity. If the system capacity cannot be increased, this can cause flooding and erosion, increase sedimentation and damage the natural habitats that accept the runoff. Further, the concentration of pollutants in the runoff can impact water quality.
A "green street" is a thoroughfare that provides water-quality treatment, retention and/or detention for some or most stormwater within the right of way through use of vegetated facilities, usually swale areas, to reduce, delay and/or filter the amount of water piped directly to outfalls. This report provides a brief discussion of reducing and treating stormwater using source control or treatment control best management practices (BMPs). BMPs are used to accommodate stormwater runoff in one or more ways:
1. Infiltration—water enters the ground directly or through pervious surfaces and percolates into the soil.
2. Retention and detention—methods to store runoff for later release. Detention measures store water for up to several days after a storm and are usually dry until the next storm. Retention measures are permanent basins that retain water.
3. Biofiltration—allow runoff to flow slowly through vegetated slopes and channels, which also capture sediment and pollutants.
4. Mechanical filtering, screening and de-sedimentation—devices that can be installed in or adjacent to thoroughfares within the public right of way that use various means to capture solids, such as litter and leaves, or fine particu-lates, such as dirt and metals.
Where thoroughfare designs can accommodate significant green space, vegetated or grass swales in the streetside or the median can be used to absorb, detain and/or filter runoff. This can reduce the necessary storm sewer capacity and treatment of the runoff.
While there are numerous practices for addressing stormwater runoff on sites, the following principles are specific to urban thoroughfare design. These principles represent an objective that either slows or delays the movement of stormwater runoff into the storm drain system, filtrates sediment and pollutants from runoff, or both. Municipalities should encourage developers to implement landscape designs and site BMPs that mitigate increases in site runoff. This reduces the runoff that reaches thoroughfares from adjacent development.
Where a rigid pavement edge is necessary, consider that swales or other filtration devices can run parallel to the street (in the streetside planting strip or in the median) but also can intersect the street at cross-angles and run between residential lots or within parks or open space.
Complete guidance in relation to storm water management is beyond the scope of this report. Designers are encouraged to seek out other references, such as those outlined at the end of this chapter, or to seek guidance from their local stormwater management agency or water quality control board. However, several guidelines can be followed to develop an initial concept for using a green approach to stormwater management:
Pervious surfaces and "green" stormwater management should be used in medians, planting strips, planters, islands, sidewalk extensions and other applicable spaces within the right of way where natural stormwater detention, filtration, or absorption is desired, soil conditions are compatible, and where a suitable design is compatible with and supportive of the desired use and appearance of the thoroughfare and surrounding context.
The growing amount of impervious surfaces in urban areas is increasing runoff and therefore the need for increased stormwater management infrastructure. It also is carrying more waterborne street pollutants needing treatment. The Environmental Protection Agency's (EPA's) Clean Water Act has authorized the National Pollutant Discharge Elimination System (NPDES), regulations for improving water quality by addressing point sources that discharge pollutants into waterways, such as stormwater collected in thoroughfares. Use of BMPs within the thoroughfare rights of way can reduce the demand for both storm sewer and treatment facility capacity and also can serve multiple functions.
Special Consideration with Snow Removal
Background and Purpose
During and after a snowstorm, most snow plows operate in emergency or "hurry-up" mode, focusing on opening up lanes for vehicles. Often, when snow is scraped from the vehicular lanes, it is piled up in the bicycle lane, parking lane, or along the sidewalk, thus making it difficult for bicyclists and pedestrians to use the facilities that have been provided for them.
Snow and ice blockages can force pedestrians onto the street at a time when walking in the roadway is particularly treacherous. Many localities that experience regular snowfalls have enacted legislation requiring homeowners and businesses to clear the sidewalks fronting their property within a reasonable time after a snowfall occurs. In addition, many public works agencies adopt snow removal programs that ensure that the most heavily used pedestrian routes are cleared, including bus stops and curb ramps at street crossings, so that snow plows do not create impassable ridges of snow. Adding to the problem, piled snow can create sight distance restrictions.
In some states snow plow operations clear the entire roadway from curb to curb. After the roadway is cleared, a smaller "snow blow" (such as brushes, pickups and plows) are used to clear pedestrian facilities.
In areas that receive regular snow, there will be tradeoffs between the recommendations of this report and the efficiency of snow plowing. Some of the recommended design elements such as curb extensions and on-street parking will affect snow plowing operations.
Related Thoroughfare Design Elements
These trade-offs need to be clearly communicated in the design process. Further, early collaboration with officials in charge of snow removal is imperative for a successful design.
The following practices are recommended regarding snow removal in the design of walkable urban thoroughfares:
American Association of State Highway and Transportation Officials. 1999. Guide for the Development of Bicycle Facilities. Washington, DC: AASHTO.
American Association of State Highway and Transportation Officials. 2004a. Policy on Geometric Design of Streets and Highways, Fifth Edition. Washington, DC: AASHTO.
American Association of State Highway and Transportation Officials. 2004b. A Guide for Achieving Flexibility in Highway Design. Washington, DC: AASHTO.
Federal Highway Administration. 2009. Manual on Uniform Traffic Control Devices. Washington, DC: FHWA.
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Institute of Transportation Engineers. 2002. Innovative Bicycle Treatments. Washington, DC: ITE.
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Transportation Research Board. 2000. Highway Capacity Manual. Washington, DC: TRB.
Transportation Research Board. 1986. NCHRP Report 282: Multilane Design Alternatives for Improving Suburban Highways. Washington, DC: TRB.
Transportation Research Board. 2003. NCHRP Report 500: A Guide for Addressing Collisions with Trees in Hazardous Locations. Washington, DC: TRB.
Rosales, Jennifer. 2007. Road Diet Handbook: Setting Trends for Livable Streets, Second Edition. New York, NY: Parsons Brinkerhoff.
United States Access Board. Accessible Public Rights-of-Way. http://www.access-board.gov/prowac/.
Sources of Additional Information
American Association of State Highway and Transportation Officials. Guide for the Design and Operation of Pedestrian Facilities. Washington, DC: AAS-HTO, 2001.
American Association of State Highway and Transportation Officials. Roadside Design Guide. Washington, DC: AASHTO, 2002.
American Association of State Highway and Transportation Officials. Highway Safety Design and Operations Guide. Washington, DC: AASHTO, 1997.
American Planning Association. Bicycle Facility Planning. APA, 1995.
City of Eugene. Arterial Collector Street Plan—Design of Transit Facilities. Eugene: Department of Public Works, November 1999.
Metro. Creating Livable Streets—Street Design Guidelines for 2040, 2nd Edition. Portland, OR: Portland Metro, 2002.
City of Los Angeles, Department of Public Works. Public Agencies Activity Stormwater Guide. Second Edition. www.lastormwater.org.
Federal Highway Administration. Flexibility in Highway Design. Washington, DC: FHWA, 1997.
Federal Highway Administration. Safety Effects of Marked vs. Unmarked Crosswalks at Uncontrolled Locations. Washington, DC: FHWA, 2002
Federal Highway Administration. Characteristics of Emerging Road Users and Their Safety. FHWA-HRT-04-103.
Grand Junction/Mesa County Metropolitan Planning Organization. Transit Design Standards and Guidelines.
Metropolitan Transit Development Board. Designing for Transit—A Manualfor Integrating Public Transportation and Land Development in the San Diego Metropolitan Area. San Diego: July 1993.
Texas Transportation Institute. Guidelines for Planning, Designing and Operating Bus-Related Street Improvements. Tri-Met. Bus Stops Guidelines. October 2002.
American Association of State Highway and Transportation Officials. Transit Vehicles and Facilities on Streets and Highways (Phase II). Future publication.
Transportation Research Board. NCHRP Report 330: Effective Utilization of Street Width on Urban Arterials. Washington, DC: TRB, 1990.
Transportation Research Board. NCHRP Synthesis 225: Left-Turn Treatments at Intersections. Washington, DC: TRB, 1996.
Transportation Research Board. TCRP 19: Guidelines for the Location and Design of Bus Stops, Washington, DC: TRB, 1996.
Transportation Research Board. Location and Design of Bus Stops, Transit Cooperative Research Program. Washington, DC: TRB, July 1996.
Transportation Research Board. TCRP Report 65— Evaluation of Bus Bulbs. Washington, DC: TRB, 2001.
Orange County Transportation Authority. Bus Stop Safety and Design Guidelines. Kimley-Horn and Associates, Inc., July 2004.
Oregon DOT. Design Guidelines for Public Transportation, 2002.
Oregon DOT. Oregon Bicycle and Pedestrian Plan.
Urban Land Institute. Dimensions of Parking, 4th Edition. Urban Land Institute, 2004.
Valley Metro, Arizona. Bus Stop Handbook: Street Improvements for Transit. Valley Metro (AZ), December 1993.
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