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5-1 This chapter presents generalized design treatments that may apply to any intersection, including A.I.I.s. Although examples of generic intersections or specific A.I.I.s may be used, the concepts in this chapter are intended to apply to a broader set of intersection configurations. The chapter presents treatments organized into these sections: ⢠General segment treatments, ⢠General intersection treatments, ⢠General crossing treatments, and ⢠Design flag treatments and techniques. Segment treatments are presented first because these refer to the approaches to the A.I.I. and are thus the first design elements a pedestrian or bicyclist encounters with an intersection. Intersection treatments are those within the boundary of the intersection, while crossings are the portions of the intersection that entail maximum exposure for pedestrians and conflicting paths for bicyclists with motor vehicles. The chapter concludes with a list of specific treatments to address the twenty design flags introduced in Chapter 4. For all treatments, sight distance for all users is an important consideration along every segment and at every node of a transportation system. Each conflict point can have sight distance issues. Static sight distance issues (e.g., landscaping, signs) and dynamic issues (e.g., moving vehicles, parked cars) should both be considered. The designer should ensure that every movement by every mode has adequate sight distance: for motorists to see pedestrians and bicyclists, for pedes- trians and bicyclists to see motorists, and for pedestrians and bicyclists to see each other. Besides sight distance and its direct effect on safety and comfort, the delay that each user experiences can affect safety and comfort. If the design and operational plan produce excessive delay for pedestrians or bicyclists relative to motorized vehicles (e.g., it takes several minutes to get from one quadrant of the intersection to another, even though there may be obvious cross- able gaps in motor vehicle traffic), pedestrians and bicyclists may identify desire lines that are not part of the design and may take shortcuts that put them at risk. What might be considered excessive will be different in various contexts, but a general rule is to avoid creating delays exceeding 30 seconds for pedestrians and bicyclists at any crossing. 5.1 General Segment Treatments The segments or approaches to an A.I.I. define the experience of a pedestrian or bicyclist when first approaching the intersection or interchange. The pedestrian or bicycle facility type should match the overall corridor facility or should be elevated to a higher-class facility at the C H A P T E R 5 Generalized Design Treatments
5-2 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges A.I.I., rather than degraded to a lower-class alternative. For example, a facility with a separate shared-use path along a roadway should not be terminated with an on-street, shared-lane facility or striped bike lane through the A.I.I. However, a facility with an on-street striped bike lane can be upgraded to a shared-use path or protected bike lane through the A.I.I. 5.1.1 Railings, Barriers, and Buffers Adding railings, barriers, and buffers to bikeways and sidewalks within A.I.I.s can increase the comfort of people walking and bicycling in these areas. These types of treatments can be especially beneficial in constrained areas where right-of-way or other spatial constraints limit the ability to offset facilities for nonmotorized users from the roadway. Where continuous rail- ings and barriers are used, such as concrete traffic barriers, utilitarian or decorative handrails, or guard rails, a shy distance of at least 2 feet from any railing is preferable in the design, with at least 1 foot in constrained locations where lane widths and other widths are also reduced to minimum dimensions. For instance, if an A.I.I. design includes a sidepath with a nominal width of 10 feet, but the sidepath will have a railing on both sides, the ultimate design should ideally incorporate 2 feet of shy distance on each side, for a total sidepath width of 14 feet (see Exhibit 5-1). Railings should be a minimum height of 42 inches next to bicycle facilities with considerations for taller 48- to 54-inch barriers if bicyclists could impact the barrier at an angle of 25 degrees or greater (1). Similar shy distances should be included in the design of sidewalks or sidepaths without rail- ings if those facilities are intended to abut adjacent travel lanes. This design acknowledges that vulnerable street users will naturally seek to put space between themselves and motor vehicle traffic and is reflected in the PLOS and BLOS analysis (see Chapter 4). Ideally, some type of street buffer should be integrated with the sidewalk or sidepath design. A recommended desirable street buffer width is 6 feet (2), with 2 feet being the minimum buffer width for sidepaths to preserve detectability underfoot for blind pedestrians. These street buffers should be landscaped or constructed of some contrasting and detectable material or surface treatment. Careful attention should be given to locating where railings and barriers start and stop in relation to intersections. These barriers can create sight distance issues for both motorized and nonmotorized users at intersections, particularly where horizontal curves, vertical crests, or steep grades are present. 5.1.2 Pedestrian and Bicycle Facility Dimensions at Bridges/Tunnels Where A.I.I.s include bridges, tunnels, underpasses, or other vertical elements immediately next to pedestrian and bicycle facilities, the design of these structures should consider shy distance and provide adequate usable widths for pedestrians and bicyclists. The usable width Exhibit 5-1. Shy distance from vertical surfaces influences the effective width of a shared-use path or sidepath.
Generalized Design Treatments 5-3 recognizes that pedestrians and bicyclists will not travel at the edge of a facility or immediately against a wall, abutment, barrier, or other structural elements. Vertical structural elements may also affect sight distance. Pedestrian and bicyclist facilities that may be affected include, but are not limited to, bike lanes, paved shoulders, separated bike lanes, shared-use paths, and sidewalks. 5.1.3 Transitions Between Bike Facility Types If on-street bicycle facilities are selected for an A.I.I., there likely will be locations where motorists must cross the bikeway to reach a ramp or change lanes before a turn. Any location where motorists must cross or enter space otherwise intended for bicyclist use represents a bicycle-vehicle conflict point. Where A.I.I.s are configured to maintain relatively high speeds and/or throughput by motorists, these zones may also be locations with a substantial speed dif- ferential between motorists and bicyclists. Where possible, bicyclists should be directed to off-street or separated bike facilities before crossings or conflict areas with complex, high-speed, or high-volume motor vehicle maneuvers (see Sections 3.2 and 3.3). These off-street or separated facilities, including shared-use paths, sidepaths, or separated bike lanes, allow for higher visibility of crossing activity using marked crossings and signal control. The transitions from on-street to off-street bicycle facilities in these conditions are similar to those suggested for roundabouts, as described in NCHRP Report 672 (3). An example configuration for a median u-turn intersection with channelized right-turn lanes is shown in Exhibit 5-2. 5.1.4 Manage Speeds In some contexts, on-street bicycle facilities may be next to high-speed motor vehicle traffic. This can be an uncomfortable environment for bicyclists. If separated bicycle facilities cannot be provided, motor vehicle speeds should be managed through design and operational strategies. Several techniques may help achieve this: ⢠Signal progression: If the A.I.I. exists along a corridor with coordinated signals, it may be possible to set the desired progression speed appropriate for the intended project outcomes. The intent is to influence driver speeds in the corridor. See Chapter 3 for a discussion relating bicycle facility type selection to vehicle speeds and traffic volumes. Exhibit 5-2. Ramping on-street bike lane to sidewalk level upstream of the crossing.
5-4 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges ⢠Deflection: Horizontal deflection, which can be introduced with a median treatment, con- trols the fastest speeds at which drivers can comfortably approach the intersection, thereby reducing speeds. Speed may be controlled at the key curves through an A.I.I., most of which include several conflict points. For example, at a DLT intersection, these points include the crossover, the displaced left-turn, and right-turns whether they are channelized or not. ⢠Narrow vehicle lane widths: Narrow lanes are effective in reducing driver speeds and reduce the right-of-way and associated crossing distances. Even if vehicle lanes are narrowed, the bicycle lane width should not be reduced. ⢠Speed feedback signs: Speed feedback signs heighten motorist awareness of their approach speeds and allow them to self-correct before the intersection. 5.2 General Intersection Treatments General intersection treatments refer to the walking or cycling experience within the bounds of the A.I.I., not including crossing locations (discussed in Section 5.3). Key considerations for intersection treatments include pedestrian wayfinding (including accessibility aspects of way- finding as defined in Chapter 4) and the ability to traverse the intersection or interchange safely and comfortably. 5.2.1 Accessibility and Wayfinding Many aspects of intersection design require attention to detail to make them accessible to all pedestrians, particularly those with mobility or vision disabilities. Pedestrian crossings at chan- nelized turn lanes can be challenging for blind pedestrians to cross unless appropriate treatments are provided. Details on the needs for locating the crossing, aligning to cross, determining when it is safe to cross, and maintaining alignment while crossing are provided in Chapter 2. Exhibit 5-3 illustrates key accessibility features at an intersection. For full guidance on ADA requirements and accessible design standards, the reader is referred to resources provided by the U.S. Access Board. The pedestrian wayfinding process is described in Chapter 2. Pedestrian wayfinding treat- ments apply to all A.I.I. designs and are classified as follows: ⢠Finding the crosswalk. These treatments are not unique to A.I.I.s and are presented in NCHRP Report 834 (4). ⢠Aligning to cross. Sometimes, crossing from one corner to another of an A.I.I. may require as many as five individual crossings, as in the case of a DLT intersection. If the crossings are straight and aligned at either end, the edges of crossings are identifiable with detectable warning surfaces, and the walkways are defined by detectable edges (such as landscaping) and lead to the crossings, this configuration can be manageable. However, if crossings change direction, such information needs to be communicated to the pedestrian. Addition- ally, most pedestrians who are blind align and use the audible cues of parallel traffic to cross. With the dispersed nature of pedestrian-vehicle conflict points at some A.I.I.s, using traffic cues for alignment may not be possible for pedestrians who are blind or have low vision. ⢠Maintaining alignment. Shorter crossings provide less opportunity for pedestrians to veer from the intended path. In this regard, the multistage crossing in Exhibit 5-4 performs well; a single-stage crossing of the mainline (i.e., no median refuge) could challenge a blind pedes- trianâs ability to maintain alignment. ⢠Additional considerations for channelized islands. Many A.I.I.s constructed to date have included channelized right-turn lanes. These channelized lanes bring their own set of acces- sibility challenges, discussed in NCHRP Report 834 (4).
Generalized Design Treatments 5-5 Depending on the configuration of the A.I.I., large channelization islands may be present. Pedestrians need clear guidance and information on where they should walk and where they should cross. Cut-through island designs can indicate to pedestrians the locations of walkways and cross- ings. However, if a cut-through is surrounded by paved areas, a blind pedestrian may not recog- nize the cut-through as the pedestrian path, and they may step up onto the paved island areas outside the pedestrian path and become disoriented on the large paved island area. Landscaping or other surfaces distinct underfoot from the intended walking path (such as grass or gravel) Exhibit 5-4. Example of well-designed multistage crossing. Exhibit 5-3. Accessibility features at intersections.
5-6 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges should be used to define the boundaries of the pedestrian walkway and give pedestrians routing cues in very large channelization islands (see Exhibit 5-5). A cut-through walkway can guide the pedestrian directly to the intended crossing point and can be angled to support pedestrians viewing oncoming vehicular traffic and potential conflicts. The channelization islands at DDIs, for example, provide the opportunity for wide walkways. The cut-through walkway should be at least 8 feet wide to accommodate pedestrians comfort- ably, including those with wheelchairs and other mobility devices. Where the cut-through is designed for a shared-use path, the preferred minimum width is 10 feet, not including shy dis- tances from vertical obstruction as discussed above. The actual curb ramp landing should be aligned perpendicular to the street centerline, which minimizes crossing distance and orients pedestrians to access ramps. Accessibility was described in Chapter 2 in the broader contexts of a projectâs land use envi- ronment. In this section, accessibility is explicitly focused on the policies related to the ADA and proposed PROWAG (5). General accessibility principles for A.I.I.s are based on those used in other intersection forms. The U.S. Access Board provides additional resources on accessibil- ity and specific requirements for Accessible Public Rights-of-Way, to which the transportation professional should refer and be familiar with. The basic principles for accessible design can be divided into the pedestrian walkway and the pedestrian crossing location. For pedestrian walkways, these considerations apply: ⢠Delineate the walkway through landscaping, curbing, or fencing to assist blind pedestrians with wayfinding. Fencing may be useful in constrained areas where there is insufficient room for landscaping or where it may be more difficult to maintain. ⢠Provide sufficient space (length and width) and recommended slopes for wheelchair users and other nonmotorized users such as people pushing strollers, bicycles, and others. ⢠Construct an appropriate landing with a flat slope and sufficient size at crossing points. For pedestrian crossing locations, these additional considerations apply: ⢠Provide curb ramps and detectable warning surfaces at the end of curb ramps and transitions to the street. ⢠Provide audible speech information messages to communicate the directionality of traffic (from the left or right) at all crossing points. Audible walk messages should be used where the spacing between APS devices is less than 10 feet. Exhibit 5-5. Example of a channelized turn lane with gravel surface material indicating distinguishing nonwalking surfaces from the pedestrian path. Source: NCHRP Report 834 (4).
Generalized Design Treatments 5-7 ⢠Provide accessible pedestrian signals with pushbutton locator tone at signalized crossings. ⢠Locate pushbuttons to be accessible by wheelchair users and adjacent to the crossing at a minimum separation of 10 feet. ⢠Align the curb ramp landing to the intended crossing direction. ⢠Crosswalk width through the intersection should be wide enough to permit people walking and using wheelchairs to pass without delay from opposing directions and accommodate bicyclists if part of a shared-use path network. Also, medians should provide sufficient storage for all nonmotorized users to wait safely when two-stage crossings are required. ⢠Pedestrians with vision, mobility, or cognitive impairments may benefit from targeted out- reach and additional informational material created with these specific users in mind. These outreach materials may include information on crosswalk placement and intended behavior and answers to frequently asked questions. For blind pedestrians, materials need to be pre- sented in an accessible format with a sufficient description of all features of the crossing. 5.2.2 Intersection Angle The angle at which two roadways intersect, whether at an intersection or at merging and diverging points, has a strong effect on motorist behavior and the approaches to and the execu- tion of turning movements within the intersection. The ability to manage these behaviors is important for the angles formed where motorist paths and bicycle or pedestrian paths intersect. Where motorists enter intersecting roadways at shallow angles (for example, in a traditional merge from a highway exit ramp), higher speeds can be maintained through the curve and into the intersected traffic stream. In some locations, such as when merging with highway traffic, maintaining speed can be important. However, in environments where vulnerable road users are present, geometry that encourages higher speeds can present a critical safety issue, especially if motorists may be moving through these points without signalization that separates move- ments in time. The intersection angle is also important for creating the shortest feasible crossing for pedes- trians and bicyclists. At points where motorists merge or diverge from through traffic, pedestrian ramps and associated crosswalks should generally be placed at the point where motor vehicle speeds will be lowest. Often, designing these crossings requires the designer to determine where the motorist has slowed for the turn without having begun accelerating into a straightaway or merging with vehicles approaching from the left. There may be component intersections within an A.I.I. that are not perpendicular for various reasons. Angled intersections are common, and even necessary, in A.I.I.s with a crossover element to the design. Where present (such as DDIs and DLT intersections), the angled inter- sections are signalized to manage conflicts between motorists and vulnerable users. Given that some intersections will be angled, the two most common options available for crosswalk design are as follows: ⢠Perpendicular Crosswalks. These crosswalks, as shown in Exhibit 5-6a, have the shortest path across the roadway. This angle also allows a pedestrian or bicyclist approaching or within the crossing to perceive approaching motorists in their peripheral vision and react if needed. This design further simplifies the placement of curb ramps and detectable warning surfaces and is generally the preferred design. ⢠Parallel Crosswalks. These crosswalks, as shown in Exhibit 5-6b, cross parallel to the driving lanes. While there is longer exposure in the roadway, this route is most direct. This design can pose wayfinding challenges for blind travelers, as well as pose difficulties in designing curb ramps and detectable warning surfaces to be in line with the direction of crossing.
5-8 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges The choice of crosswalk design depends on the context. As a starting point, designers should begin with perpendicular crosswalks at uncontrolled crossings and parallel crosswalks at con- trolled crossings. Factors that could alter the crosswalk type include pedestrian sight distance, ADA considerations, right-of-way and other physical constraints, and critical pedestrian signal phases affecting delay for other users. 5.2.3 Channelized Turn Lanes Channelized turn lanes, principally channelized right-turn lanes, are a common feature of many intersections and A.I.I.s. In the focus group and survey research conducted in developing this guide, feedback from pedestrians was heavily critical of channelized turn lanes. Participants shared the expectation that drivers would rarely yield within channelized turn lanes. Challenges with channelized turn lanes for nonmotorized users can include the following: ⢠Channelized turn lanes may create sight distance issues for crossing pedestrians; ⢠Channelized turns are typically taken at higher speeds than conventional right-turns at the intersection, increasing the required sight distance and potential severity of a conflict; ⢠Channelized turn lanes render audible clues difficult or impossible for pedestrians who are blind; and Exhibit 5-6 (a, left). Crosswalk variations for a skewed intersection. (b, right). Crosswalk variations for a skewed intersection.
Generalized Design Treatments 5-9 ⢠If decision points are not properly segregated for the motorist (pedestrian yielding versus merging into the travel lane), the motorist may be looking for gaps in traffic and fail to yield to crossing pedestrians. 5.2.3.1 Geometric Configuration of Channelized Turn Lanes A channelized turn lane should limit motor vehicle speeds. This can be done by designing the intersecting angle with the receiving roadway to be between approximately 55 to 60 degrees, as shown in Exhibit 5-7. Besides the speed-reducing effect of the higher angle, the view angles for drivers scanning for pedestrians and looking to the left for conflicting traffic are improved. A channelized turn lane should also separate decision points from one another. A driver should be focused on the decision at the vehicle-pedestrian conflict point before they are looking left to judge and make a decision regarding the vehicle-vehicle conflict point. A channel ized lane with at least one vehicle-length of storage between the vehicle-pedestrian and vehicle-vehicle conflict points provides this separation (consistent with the design of entry approaches at modern roundabouts). 5.2.3.2 Traffic Control of Channelized Turn Lanes NCHRP Report 562: Improving Pedestrian Safety at Unsignalized Crossings, supplemented with research on the rectangular rapid-flashing beacon (RRFB), provides guidance on improving pedestrian safety at unsignalized crossings (6). The NCHRP report provides tools for devel- oping appropriate crossing treatments based on vehicle speeds, traffic volumes, and the anticipated number of pedestrian crossings. Also, NCHRP Report 834 provides guidance on designing channelized turn lanes to be accessible to people with vision disabilities (4). Potential crossing treatments may include any of the following or, in some cases, a combination of two or more of the following: ⢠Pavement markings, ⢠Signing, ⢠Flashing beacons, ⢠RRFBs with audible indications, Exhibit 5-7. Channelized right-turn design. Source: NCHRP Report 834 (4).
5-10 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges ⢠Pedestrian hybrid beacons (PHBs) with accessible pedestrian signals, ⢠Raised crosswalks, and ⢠Fully signalized crossings that are coordinated with the main intersection and with accessible pedestrian signals. 5.2.3.3 Replace Channelized Turn Lane with Conventional Turn Lane Where channelized turn lanes create challenging safety issues, removing the channelized turn lane may be an option. Removing channelization may degrade vehicular operations where there is a high volume of turns. For on-street bicyclists, some design provisions must still be provided where turning drivers cross the paths of through bicyclists (i.e., the âright hookâ conflict). For pedestrian crossings, removing the channelization can reduce the number of distinct crossing stages and associated delay. Removing the channelization consolidates pedestrian-vehicle conflict points in space. Cross- walk length may increase, which may have an undesirable effect on signal timing and cycle length. However, removing the channelized turn lane reduces the number of crossing stages for pedestrians, which may result in a net reduction in pedestrian delay. The designer should weigh several factors, including the signal timing effects of including right-turns in the main inter- section, the effects on operational capacity in the presence of heavy right-turns, the effects on large vehicles, and the safety and comfort for bicyclists. Where channelized right-turns are provided with bypass lanes, such as at DLT intersections, the angle of visibility for drivers to yield as they merge back into traffic can be challenging; if a pedestrian crossing is provided in this location, the designer should consider the traffic control device and restriction of right-turn-on-red. 5.2.3.4 Other Treatment Options for Channelized Turn Lanes Other treatment options for channelized turn lanes include the following: ⢠Restricting right-turns-on-red so drivers will have no incentive to position themselves for an opportune right-turn until they have a green signal; ⢠Providing a marked stop line or yield line before the marked pedestrian crossing (the decision for which depends on State laws regarding stopping for or yielding to pedestrians); ⢠Adding a raised crosswalk in the channelized turn lane to geometrically control vehicle speeds (See Exhibit 5-8); Exhibit 5-8. Channelized turn lane with raised crosswalk to slow vehicular traffic. Source: NCHRP Report 834 (4).
Generalized Design Treatments 5-11 ⢠Providing adequate corner sight distance at the intersection from the stop bar to separate the two areas in space; and ⢠Considering queue storage for a motorist to wait between the crossing and conflicting traffic flow when wanting to turn right on red (providing separation between driver decisions). 5.2.4 Right-Turn Treatments for Bicyclists Where bicyclists cannot be separated from motorists upstream of conflict points, the design should use treatments such as green pavement to draw attention to conflict areas. Weaving and merging zones where motorists can enter bicyclist space should be as short as practicable to minimize bicyclist exposure and can help control vehicle speeds where these conflicts occur. Exhibit 5-9 shows several options for how green conflict markings can be used where turning motorists may cross an on-street bike lane to access a ramp or turn. The best option will depend on the context within the approaching roadways and intersection, and the intended design userâs risk tolerance. This design may be supplemented with signage to advise motorists and define right-of-way in weaving areas. One such sign used by the MassDOT is R10-15 alt., illustrated in Exhibit 5-10, which advises motorists to yield to pedestrians and bicyclists in an adjacent parallel facility (7). 5.2.5 Left-Turn Treatments for Bicyclists When an on-street bicycle facility is provided, or when confident bicyclists adopt a vehicular cycling approach to the intersection, bicyclists may need to cross the motor vehicle travel lanes to use the left-turn lane(s). In some designs, this crossover also puts a bicyclist in a bike lane with motor vehicles on both sides or in no bike lane at all. Exhibit 5-9. Marking right-turn lane/bike lane conflict zone with green pavement for a crossover (left) and for a bike signal and keep the bikes far to the right (right). Exhibit 5-10. Turning vehicles yield to bicycles and pedestrians sign (R10-15 alt.). Source: MassDOT (7).
5-12 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges This design feature is not exclusive to A.I.I.s; it is a feature of any intersection with left-turn lanes. This left-turn option minimizes out-of-direct travel but may come at the expense of sus- tained exposure, conflict points, and stressful riding conditions. This design flag is presented and discussed in Section 4.4.16, Lane Change Across Motor Vehicle Travel Lanes. A two-stage turn queue box allows bicyclists to make left-turns in two movements without crossing over motorist travel lanes to reach a left-turn lane. The turn queue box should be properly designed per FHWA Interim Approval IA-20 (8) and be out of the path of through bicycle traffic (Exhibit 5-11). When the appropriate phase turns green, the bicyclists may make the second part of the movement through the intersection. 5.2.6 Provide Separation/Protected Intersection Concept Separation for bicyclists can take the form of a separated bike lane or a shared-use path. The key elements of this treatment include a refuge island for bicyclists that controls effective turn radii and turning speeds of motor vehicles, a crossing set back from the corner to increase visibility and reaction time, and a queuing area for turning motorists to yield to pedestrians and bicyclists. An example of a protected intersection concept applied to a MUT intersection is shown in Exhibit 5-12. 5.3 General Crossing Treatments Absent grade-separated facilities for nonmotorized users, such as overpasses or underpasses, A.I.I.s will inevitably include locations where nonmotorized paths and motorist paths must cross. These locations should be designed following the principles outlined in Chapters 2 and 3 to reduce the likelihood of crashes and the severity of any crashes that do occur. An important determination in the design of an A.I.I. is the location of the crossings. In tra- ditional intersections, the crossing locations are generally predetermined, but locating crossings in A.I.I.s can require more complex analysis. Maximizing the operations and safety of crossings Exhibit 5-11. Example of two-stage turn queue boxes at a DLT.
Generalized Design Treatments 5-13 could require significant geometric changes to the initial roadway design to provide adequate sight distance and encourage the desired yielding behavior. Some A.I.I.s may also require careful coordination of signals for pedestrians and bicyclists. The design for pedestrians and bicyclists must occur as early in the design phase as possible and include input from both roadway and traffic designers. Once the higher-level design considerations are addressed, the design of individual ele- ments and crossings requires consideration of treatments to further reduce speeds, provide adequate perception-reaction times, and heighten the visibility of vulnerable road users to motorists. In addition, nonmotorized users should also be readily able to perceive and react to any motorist approaching in a threatening way. Design treatments recommended for loca- tions where bicyclists and pedestrians cross paths with motorists include recessed or raised crossings, high-visibility pavement markings and/or green pavement treatments, signalized crossings, pedestrian-activated beacons, properly sized refuge islands, and designing for weaving or merging zones. 5.3.1 Types of Crossings The complexity of signalization and associated motor vehicle movements within an A.I.I. may require that pedestrian and bicyclist crossings be performed in stages. To the extent pos- sible, the number of stages should be minimized, because each stage and intermittent waiting period can increase the delay to pedestrians and bicyclists, which further discourages travel by these modes. Multiple stages and long waiting periods may also increase the likelihood that nonmotorized road users will engage in risk-taking behavior. As noted in Chapter 2, when the delay exceeds 30 seconds, pedestrians are more likely to engage in risk-taking behavior (2). This behavior can be exceptionally dangerous in some crossings within an A.I.I., where nonmotorized users may not see or correctly anticipate the direction, timing, or speed of approaching motor vehicle traffic. Multistage crossings take various forms in terms of their operations: ⢠Single-Stage Crossing with Multistage Option: In these cases, the crossing is timed as a single-stage crossing using standard MUTCD guidance (9), but a refuge island is provided to allow an optional multistage crossing by pedestrians walking slower than the design walking speed for the crossing or by pedestrians who enter the crosswalk during Flashing Donât Walk. Exhibit 5-12. Example of protected intersection components at an MUT intersection.
5-14 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges ⢠Multistage Crossing: In these cases, the crossing is broken into one or more components, and each crossing is controlled separately. The phases for each crossing generally occur within the same signal cycle, although phases may span the end of the first cycle and beginning of the next cycle. These crossings are distinct from multicycle crossings, discussed below. ⢠Coordinated Signalized Crossing Stages: Although stages have separate phases, the phases are coordinated to reduce or eliminate the delay associated with the crossing between refuge points. The geometric spacing between crossings can often play a critical role in how well stages can be coordinated, and coordination may be possible only in one direction of travel. ⢠Combination of Controlled and Uncontrolled Crossings: Ideally, in these crossings, the uncontrolled crossing has low delay but should consider how signal timing of the A.I.I. and adjacent signals may result in platooning or volumes that affect this uncontrolled delay. ⢠Pedestrian-Only and/or Bicycle-Only Phase Crossings: Pedestrians or bicyclists cross on signal phases timed to be separate from conflicting motor vehicle signal phases. ⢠Multicycle Crossings: These are crossings where a pedestrian or bicyclist cannot cross the intersection in one cycle, and the same signal phase is used in consecutive cycles to complete the crossing. This can be common at intersections with wide medians/deep refuge islands where the pedestrian signal timing only gives clearance for crossing one-half of the roadway at a time. These produce excessively long delays for pedestrians and bicyclists (by definition, delays exceed the cycle length) and should be avoided. Where crossings must be staged, the design should consider the signal phasing and timing in the location and layout of pedestrian refuges and channelization for motorists. The designer should evaluate tradeoffs among the following: ⢠Inducing pedestrians to make long crossings with the additional signal timing and phases needed to ensure pedestrian clearance of the crossing; ⢠Creating a series of shorter crossings and the additional right-of-way required to construct refuges of the appropriate size at any location where pedestrians and bicyclists may dwell; ⢠Establishing single-stage exclusive crossings of lane groups where motor vehicle movements (including permissive turns) will not conflict with the nonmotorized movements, provided that the duration is adequate to ensure pedestrian clearance; and ⢠Creating geometric alterations to the roadway design that will help lessen delays between stages. Multistage crossings can be safer than single-stage crossings, particularly at uncontrolled crossings where a median refuge breaks the crossing into shorter distances and where the number of conflicts that must be processed by the crossing user is lessened. However, if a multi- stage crossing results in excessive delays, or if the multistage crossing directs crossing users to out-of-direction locations, the crossing user may engage in more risk-taking behavior to reduce their delay or crossing distance. Providing efficient operations for multistage crossings is an important element in achieving the desired user behavior and safety benefits. Understanding the details of the geometric design, signal timing, and expected vehicle platooning are often critical to providing the most efficient operations. 5.3.2 Multiple-Threat Locations Multiple-threat conditions can exist at crossings where vulnerable users must traverse two or more travel lanes. These crossings may be uncontrolled or signalized crossings with per- missive conflicts. In a multiple-threat crash, the motorist in the lane closest to the crossing vulnerable user has stopped to yield, the vulnerable user has entered the crossing, and due to motorist inattention or poor sightlines, a motorist approaching in the adjacent lane does not stop and strikes the vulnerable user in the crossing. In a multiple-threat condition, the second
Generalized Design Treatments 5-15 motoristâs view of the vulnerable user is not only obstructed by the first vehicle (Exhibit 5-13), but the vulnerable userâs view of the approaching second vehicle is also blocked by the first vehicle (Exhibit 5-14), preventing the vulnerable user from stopping in time to avoid the crash. This is especially true for children and people in wheelchairs whose eye height is lower, preventing them from seeing beyond the stopped vehicle until they have entered the adjacent travel lane. In addition, people who are blind or have low vision may not hear the second vehicle approaching due to the sound of the yielding vehicle. If a multiple-threat condition is present, the MUTCD provides for yield line or stop line set back 20 to 50 feet from the cross- walk to reduce the likelihood of obscured lines of sight [see MUTCD Figure 3B-17 (9)]. Because A.I.I.s can include multilane crossings, the potential for multiple-threat conditions may be present in one or more locations. The design should either eliminate locations where multiple-threat crashes could occur or phase-separate the crossing. Where these conditions cannot be eliminated or fully phase-separated, the design should, at minimum, include treat- ments that alert motorists to vulnerable users in the crossing, such as raised crossings and/or flashing beacons. Setting the stop or yield line back from the crossing can also help maintain sightlines between approaching motorists and crosswalk users. Exhibit 5-14. Multiple-threat crash â Pedestrianâs view of approaching vehicle is blocked by yielding motorist. Exhibit 5-13. Multiple-threat crash â Second motoristâs view of the pedestrian is blocked on crosswalk approach by yielding motorist.
5-16 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges Multiple-threat conditions may also exist at signalized locations when permissive turns or right-turn-on-red are allowed by multiple left- or right-turn lanes. Where these turns are per- mitted across crosswalks showing pedestrian Walk indications, visibility of pedestrians can be reduced along with the ability to yield without affecting through traffic. It is recommended that this condition not be introduced and that pedestrian Walk indications do not coincide with permissive turns or right-turn-on-red across the crosswalk. In these cases, protected turns for motorists or separate phases for permissive turns and pedestrian movements are recommended. 5.3.3 Offset Crossings Where sidewalks, sidepaths, or separated bike lanes are aligned parallel to motor vehicle travel lanes, the designer should consider enhancing any crossings where motorists may turn left or right across these nonmotorized facilities. Crossings offset from the parallel motor vehicle lanes, also sometimes called recessed cross- ings, have been shown to improve motorist yielding rates (as summarized in 7). These crossings are commonly located 6 to 20 feet from the travel lanes, with higher offset distances correspond- ing to higher vehicular speeds along the mainline. This offset distance allows for additional perception and reaction time by motorists encountering bicyclists or pedestrians in the crossing, and it provides a place for the turning vehicle to queue at the crossing that is clear of the parallel motor vehicle traffic. Offset crossing locations are a standard feature of roundabouts due to their ability to separate decision points for drivers (3). In addition to offsetting the crossing location, sightlines between drivers and nonmotorized users should be maintained to allow motorists a clear view of nonmotorized users in or approaching the crossing. 5.3.4 Raised Crossings Crossing locations can be augmented by raising the crossing, as shown in Exhibit 5-15, in which case a raised crossing is combined with an offset crossing. Raised crossings slow motorist approach speeds at the crossing and elevate users in the crosswalk to increase their visibility to motorists. Raised crossings further communicate right-of-way priority at the crossing and increase safety for pedestrians and bicyclists. Exhibit 5-15. Offset raised crossing.
Generalized Design Treatments 5-17 5.3.5 Pavement Markings Pavement markings are key to communicating right-of-way between users and alerting motorists and nonmotorists to the possible presence of other intersection users. High-visibility crosswalk markings have been shown to increase motorist yield rates and yielding distance and increase pedestrian scanning for vehicle conflicts before crossing (10). These markings should be used in any location in an A.I.I. where a sidewalk, sidepath, or shared-use path crossing intersects a vehicle path. At locations where on-street bikeways or separated bike lanes cross an intersecting travel lane, the designer should consider the use of green conflict markings, as illustrated in Exhibit 5-16. These crossing bars alert motorists to the intersecting bikeway and highlight the conflict zone. The geometry of the bars typically aligns with any adjacent high-visibility crosswalk markings and extends the full width of the bike facility. 5.3.6 Signalized Crossings In cases with high volumes for any mode, locations where sidewalks, sidepaths, or shared-use paths cross a motor vehicle path ideally should be signalized. Crossings should also be signal- ized when there is a significant safety hazard created by leaving the crossing uncontrolled, such as in locations with limited sight distance, crossings with multiple lanes in a single direction, or crossings where motor vehicle speeds are likely to exceed 20 mph. Street-level bike lanes, whether conventional or separated, that follow the alignment of travel lanes can typically follow travel lane signalization, provided that the clearance time is calculated for the slower speed of bicyclists (12 to 18 mph). If this bicycle clearance time is not possible due to a combination of the length of the crossing, maximum allowable yellow clearance time, and bicycle speeds (which may depend on vertical grades of the intersection), additional mitigation (e.g., mid crossing refuge spaces) is likely necessary. Signalized crossings that separate signal phases, so motorists do not move concurrently with pedestrians or bicyclists, reduce the likelihood of crashes. In contexts with significant safety concerns or moderate to high nonmotorized (pedestrian or bicycle) volumes, signals should be designed to avoid concurrent vehicle phases with conflicting nonmotorized crossings. Designers Exhibit 5-16. Street-level bike lane at side street/ramp entry with green conflict markings (left) and sidewalk level separated bike lane at side street/ramp entry with green conflict markings (right).
5-18 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges should provide adequate pedestrian clearance time to ensure that pedestrians are not within the crossing when conflicting traffic movements are released. Pedestrian signals with countdown displays are recommended for conveying remaining phase time to crosswalk users in compliance with MUTCD requirements (9). These countdown dis- plays often provide cues for drivers and on-street bicyclists regarding the remaining vehicular green time. However, sometimes pedestrian phases end earlier than the concurrent vehicular phase. This can create potential safety issues for both drivers and cyclists at the end of either phase. Designers should consider the potential safety impacts on other users when concurrent pedestrian and vehicular phases do not end simultaneously. These considerations may also affect a decision to allow or not allow a pedestrian signal head to be visible to other users. Where full signals are not practicable, other crossing treatments, such as raised crosswalks, additional crossing signs/warnings, RRFBs, and PHBs, should be considered. 5.3.7 Refuge Islands Where longer crossing distances or signalization require pedestrians and bicyclists to cross in stages, refuge islands should be provided for vulnerable users to wait. These refuge islands should be sized depending on the volume of expected users but should be no less than 5 feet wide (perpendicular to the direction of pedestrian and bicyclist travel) (5) and preferably at least as wide as the crosswalk to which they connect, which is at least 6 feet wide per the MUTCD (9). A refuge depth of 10 feet in the direction of pedestrian and bicyclist travel accommodates bicycles with trailers or with tagalong extensions; it also increases the waiting space and comfort for pedestrians who must queue on the island. The minimum refuge depth in the direction of pedestrian and bicycle travel is 6 feet, which is the minimum to allow two sets of detectable warn- ings (each 2 feet in depth) plus a gap between them of 2 feet. The 6-foot minimum depth is also the depth needed for the physical length of a standard bicycle or a person pushing a stroller (see Exhibit 5-17). Where higher volumes of users are expected or are congregating from crossings in multiple directions, the refuge space should be designed to fit all users. There may be a tradeoff in terms of overall travel time and the possibility of needing to split the crossing into multiple stages if the refuge dimensions are large. The context of the location, the intended operation of the intersection, and attendant tradeoffs among modes should be considered when determining the ultimate refuge island dimensions. 5.3.8 Long Single-Stage Crossings Long single-stage crossing opportunities can be challenging for pedestrians when there are multiple lanes and traffic from opposing directions. As the number of lanes increases, the differ- ence between walkable distance by an average pedestrian and a slower pedestrian increases, thus making the crossing more difficult for slower pedestrians. Longer crossings without refuges also introduce the possibility for pedestrians with vision disabilities to veer considerably from their traveled path within the crosswalk. One solution is to provide pedestrian islands to break the crossing up and to provide refuge. The pedestrian delay and signal timing tradeoffs associated with this design decision are dis- cussed in later chapters. The refuge islands should be sufficiently wide to meet ADA accessibility requirements and, ideally, best practices to provide room for a person with a bicycle; however, any median or refuge that is substantially wider may create extra crossing time for pedestrians. When confronted with the tradeoff between multiple shorter crossings versus fewer longer crossings, using detailed performance measures can help to determine which option produces the desired result.
Generalized Design Treatments 5-19 There is no universally optimal solution for providing pedestrian crossings along the dimen- sions of operations, delay, and safety. However, the tradeoffs presented here should allow the designer to consider the design option that matches the desired performance outcome. 5.4 Design Flag Treatments and Techniques Chapter 4 introduced a set of twenty design flags that may affect comfort and safety for pedes- trians and bicyclists. This section lists potential treatments and techniques for each of the twenty flags. These treatments and techniques can be applied without changing the overall design concept. 5.4.1 Motor Vehicle Right-Turns Design techniques and treatments can include ⢠Providing a stop bar before the marked pedestrian crossing. ⢠Providing adequate sight distance at the intersection from the stop bar. ⢠Including space for queue storage for a vehicle to queue in-between the crossing and con- flicting traffic flow, when waiting to turn right on red (providing separation between driver decisions). ⢠Restricting right-turns-on-red. Exhibit 5-17. Minimum and preferred widths for refuge islands.
5-20 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges 5.4.2 Uncomfortable/Tight Walking Environment Design techniques and treatments can include ⢠Widening the sidewalk. ⢠Illuminating the walking environment. ⢠Increasing the size of channelization islands and corner areas. ⢠Providing vertical separation between pedestrians and vehicles. ⢠Providing horizontal separation (buffers) between pedestrians and vehicles. 5.4.3 Nonintuitive Motor Vehicle Movements Design techniques and treatments can include ⢠Designing the approaching path to face the initial direction of opposing traffic. ⢠Providing signing that is viewable and understandable to the intended users, as well as appro- priate speech messages for any accessible pedestrian signals or audible information devices. ⢠Providing pavement marking at the entrance to the crossing that indicates which direction a pedestrian or bicyclist should look to view oncoming traffic. ⢠Choosing different geometric features of the design to minimize or eliminate movements from unexpected directions. 5.4.4 Crossing Yield-Controlled Or Uncontrolled Vehicle Paths Design techniques and treatments can include ⢠Providing signalized crossings. ⢠Providing stop-controlled crossings. ⢠Reducing vehicle speed through curvatures. ⢠Installing raised crosswalks to reduce vehicle speed. 5.4.5 Indirect Paths Design techniques and treatments can include providing the following: ⢠Direct crossing opportunities with a dedicated pedestrian phase, if necessary. ⢠Midblock crossing before the intersection to address an otherwise indirect path. ⢠Grade-separated pedestrian and bicycle facilities, depending on the context and the origin- destination patterns for pedestrians and bicyclists. 5.4.6 Executing Unusual Movements Design techniques and treatments can include ⢠Re-aligning pedestrian/bicycle movement to make them more intuitive. ⢠Constructing dedicated pedestrian or bicycle facilities. ⢠Following the design process to meet expectations for people walking and biking. 5.4.7 Multilane Crossings Design techniques and treatments can include ⢠Reducing the number of travel lanes. ⢠Providing two-stage crossings to reduce the number of lanes and travel directions crossed at one time. ⢠Providing signalized or stop-controlled crossing. ⢠Installing raised crosswalks to reduce vehicle speed.
Generalized Design Treatments 5-21 5.4.8 Long Red Times Design techniques and treatments can include ⢠Reducing the overall cycle length. ⢠Modifying the phase sequence to reduce the total crossing time. (This particularly applies for priority movements because improvements in travel time for one origin-destination pattern may result in longer crossing times for other movements.) 5.4.9 Undefined Crossings at Intersections Design techniques and treatments can include ⢠Striping biking pathways through an intersection to identify where drivers are entering the designated path of bike travel. ⢠Where off-street bicycling facilities are provided, placing the bike crossing and the pedestrian crossing next to one another to reduce undefined space. ⢠Designing two-stage left-turn queue boxes with queuing space for multiple bicyclists. [Two-stage turn queue boxes are allowed by and subject to FHWA Interim Approval IA-20, Optional Use of Two-Stage Bicycle Turn Boxes (8).] 5.4.10 Motor Vehicle Left-Turns Design technique and treatments can include ⢠Converting permissive left-turn movements into protected left-turn movements with a dedi- cated signal phase. (At RCUTs, an option is to remove left-turns at the intersection.) ⢠Providing queue storage for at least one vehicle between the pedestrian crossing and the end of the channelized turn lane to separate motorist decision points. ⢠Using a traffic control signal to control the channelized turn movement. ⢠Removing the channelized turn lane. 5.4.11 Intersecting Driveways and Sidestreets Design technique and treatments can include ⢠Reducing the number of driveways through access management. ⢠Controlling vehicle speeds at driveways through curvature or vertical elements. ⢠Providing signalized or stop-controlled crossings at driveways. 5.4.12 Sight Distance for Gap Acceptance Movements Design technique and treatments can include ⢠Designing vertical obstructions, such as bridge abutments, tall landscaping, and signal cabinets to be positioned outside of necessary sight triangles. ⢠Establishing horizontal and vertical alignments that provide the necessary sight distance. 5.4.13 Grade Change Design technique and treatments can include ⢠Constructing a dedicated protected bike lane on grade sections. ⢠Constructing a multiuse path on grade sections. ⢠Reducing vehicular speeds.
5-22 Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges 5.4.14 Riding in Mixed Traffic Design technique and treatments can include ⢠Separating bicyclists from motor vehicles through dedicated protected lanes. ⢠Designing for lower motor vehicle speeds where bicyclists and motorists interact. 5.4.15 Bicycle Clearance Times Design techniques and treatments can include ⢠Reducing the number of lanes to cross. ⢠Reducing lane widths. ⢠Reducing median widths. ⢠Moving ramps closer to the crossover. ⢠Providing refuge for bicyclists. ⢠Installing bicycle dilemma zone detection to extend the transition of signal phases when necessary. ⢠Providing a separate bicycle signal with a dedicated indication of required clearance time. 5.4.16 Lane Change Across Motor Vehicle Travel Lanes Design techniques and treatments depend on the crossover movement, but can include the following: ⢠Designing for bicyclists to use ramps to sidewalks or shared-use paths and cross in a crosswalk. ⢠Designing for bicyclists to use a two-stage bicycle left-turn queue box with adequate room to maneuver and wait. ⢠At RCUTs, designing for bicyclists to make a through movement with a channelized direct bicycle crossing (only feasible absent a pedestrian âZâ crossing). ⢠Clearly marking the entry to the crossover area. ⢠Design for low motorist speeds (below 20 mph) through a crossover area by reducing radii or implementing speed-reducing treatments. 5.4.17 Channelized Lanes Design techniques and treatments will depend on the channelized lane, but can include the following: ⢠Designing for bicyclists to use ramps onto sidewalks or shared-use paths and cross in a crosswalk, instead of traveling as vehicles. ⢠Designing for bicyclists to use a two-stage bicycle left-turn queue box with adequate room to maneuver and wait, instead of making a direct left-turn with motorized traffic. ⢠At RCUTs, designing for bicyclists to make a through movement with a channelized direct bicycle crossing (only feasible absent a pedestrian âZâ crossing). ⢠Designing for low motorist speeds (below 20 mph) in channelized lane areas by reducing curve radii. 5.4.18 Turning Motorists Crossing Bicycle Path Design techniques and treatments can include ⢠Providing design treatments for vehicle storage between the pedestrian crossing and vehicle merge, thereby separating driver decision points.
Generalized Design Treatments 5-23 ⢠Installing a signal to control the channelized movement. ⢠Designing channelization to manage vehicular speeds through the use of compound curves. ⢠Implementing raised crossings at the location within the channelized turn where motorist speeds are lowest. ⢠Removing channelization. 5.4.19 Riding Between Travel Lanes, Lane Additions, or Lane Merges Design techniques and treatments can include ⢠Replacing merge areas with stop- or yield-controlled movements. ⢠Constructing separate protected bike lanes or multiuse paths. ⢠Reducing vehicle speeds in conflict areas. 5.4.20 Off-Tracking Trucks in Multilane Curves Design techniques and treatments can include ⢠Constructing separate protected bike lanes or multiuse paths. ⢠Increasing lane widths in curved areas. ⢠Using striped vane islands to separate vehicle lanes. 5.5 References 1. AASHTO. 2012. Guide for the Development of Bicycle Facilities, Fourth Edition. AASHTO, Washington, DC. 2. TRB. 2016. Highway Capacity Manual, Sixth Edition. Transportation Research Board of the National Acad- emies, Washington, DC. 3. Rodegerdts, L., J. Bansen, C. Tiesler, J. Knudsen, E. Myers, M. Johnson, M. Moule, B. Persaud, C. Lyon, S. Hallmark, H. Isebrands, R. B. Crown, B. Guichet, and A. OâBrien. 2010. NCHRP Report 672: Round- abouts: An Informational Guide. Second Edition. Transportation Research Board of the National Academies, Washington, DC. 4. Schroeder, B. J., L. Rodegerdts, P. Jenior, E. Myers, C. Cunningham, K. Salamati, S. Searcy, S. OâBrien, J. Barlow, and B. L. Bentzen. 2016. NCHRP Report 834: Crossing Solutions at Roundabouts and Channel- ized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook. Transportation Research Board of the National Academies, Washington, DC. 5. United States Access Board. 2011. Proposed Guidelines for Pedestrian Facilities in the Public Right-of-Way (PROWAG). https://www.access-board.gov/guidelines-and-standards/streets-sidewalks/public-rights- of-way/proposed-rights-of-way-guidelines. 6. Fitzpatrick, K., S. Turner, M. Brewer, P. Carlson, B. Ullman, N. Trout, E. S. Park, J. Whitacre, N. Lalani, and D. Lord. 2006. NCHRP Report 562: Improving Pedestrian Safety at Unsignalized Crossings. Transportation Research Board of the National Academies, Washington, DC. 7. MassDOT. 2015. Separated Bike Lane Planning and Design Guide. https://www.mass.gov/lists/separated- bike-lane-planning-design-guide. MassDOT, Boston, MA. 8. FHWA. Interim Approval for Optional Use of Two-Stage Bicycle Turn Boxes (IA-20). https://mutcd.fhwa.dot.gov/ resources/interim_approval/ia20/index.htm. FHWA, Washington, DC. Accessed March 28, 2019. 9. FHWA. 2009. Manual on Uniform Traffic Control Devices (MUTCD). U.S. Department of Transportation (USDOT), Washington, DC. 10. Mead, J., C. Zegeer, and M. Bushell. 2014. Evaluation of Pedestrian-Related Roadway Measures: A Summary of Available Research. Highway Safety Research Center, Pedestrian and Bicycle Information.
