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21 C H A P T E R 4 This chapter presents an overview of the design elements that are specific to roundabouts. 4.1 Geometric Design This chapter presents the proposed best practices for the design of roundabouts, apply- ing the wayfinding and crossing tasks discussed in Chapter 3 to specific applications at roundabouts. Figure 4-1 shows the typical dimensions and placement of a crosswalk at a roundabout. Crosswalks pass through the splitter islands, creating a two-stage crossing for pedestrians. They are set back from the yield line by one or more car lengths to: ⢠Shorten crossing distance (lane widths generally flare out approaching the circulatory roadway), ⢠Separate vehicle-vehicle and vehicle-pedestrian conflict points, ⢠Help pedestrians distinguish between exiting traffic and circulating traffic, and ⢠Allow the second entering driver to devote attention to crossing pedestrians while waiting for the driver ahead to enter the circulatory roadway (Rodegerdts et al., 2010). At most roundabouts in the United States, crosswalks have been set back one car length from the circulatory roadway on both the entry and the exit. This section presents several crosswalk configuration options and associated trade-offs. There are three general principles for developing design solutions to optimize wayfinding information for people who rely on nonvisual information: 1. Landscaping, fences, or other features should restrict the ability of pedestrians to cross at locations other than crosswalks, or at least make it very clear where crossing is not intended, and provide guidance to the crosswalk location. 2. Curb ramps should be oriented so that the running slope is in the same direction as the crosswalk and/or the edges of landscaping or ramps should be aligned in the direction of travel on the crosswalk. 3. The far side of the crosswalk and any channelization and splitter islands should be aligned with the nearside ramp and should be designed to compensate for the expected error in the crossing angle. Specific treatments to maximize wayfinding information will be described and illustrated in this section, and their potential benefits for pedestrians who are blind will be explained. Design Principles for Pedestrian Access at Roundabouts
22 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook 4.1.1 Crosswalk Location and Angle Options The geometric design of a crosswalk can directly influence its effectiveness, regardless of the type of traffic control devices used at that crosswalk. There are several conflicting challenges to balance: ⢠The crosswalk should be located conveniently close to the roundabout to minimize out-of-direction travel for pedestrians. Pedestrians are increasingly likely to cross closer to the roundabout if the designated crossing location is too far away, insufficient channelization is provided to encour- age crossing at the appropriate location, and the pedestrian does not perceive a risk of crossing away from the designated location. ⢠Positive wayfinding guidance to the crosswalk is critical, regardless of location. The curvilinear nature of roundabouts makes it substantially more difficult for a pedestrian with vision disabil- ities to locate the appropriate crossing location and to maintain the correct heading through the crosswalk. Positive channelization also assists pedestrians without vision disabilities by encouraging them to cross at the appropriate crossing location and discouraging them to cross at inappropriate locations. This is a requirement in PROWAG-NPRM. ⢠The crosswalk should be located such that approaching drivers have time to see a pedestrian in it, react and apply their brakes, and stop their vehicles before reaching the crosswalk. This distance, which is a function of speed, is referred to as stopping sight distance and has numerous applications in roadway design. Stopping sight distances are provided in the Green Book (Table 3-1, Stopping Sight Distance on Level Roadways, and Table 3-2, Stopping Sight Distance on Grades). A portion of Table 3-1 has been reproduced as Table 4-1. Figure 4-1. Typical crosswalk dimensions and features of a single-lane roundabout. Figure 4-1 shows a crosswalk at a roundabout with a number of specific design features called out. The crosswalk passes through a splitter island, creating a two-stage crossing. The crosswalk is set back one car length (20 ft) from the circulatory roadway, the sidewalk is 10 ft wide, the crosswalk is marked and signed, detectable warning surfaces are used in the splitter island and on the outside of the roadway, the splitter island is cut through (pedestrians do not travel up and down a ramp), and the splitter island is a minimum of 6 ft wide at the crosswalk location.
Design Principles for Pedestrian Access at Roundabouts 23 ⢠For crosswalks with traffic control device, minimum stopping sight distance needs to be pro- vided. MUTCD specifies a minimum sight distance for the visibility of traffic signal heads in Table 4D-2. The distances are derived from the stopping sight distance (shown in Table 4-1) and the assumed queue length for a short signal cycle length. Therefore, the distances are greater than the stopping sight distance values shown in Table 4-1. Section 4D.12 of MUTCD states that the distances in Table 4D-2 should be provided for traffic signals (unlikely at a roundabout crosswalk) and Section 4F.02 of MUTCD notes that Section 4D.12 is applicable to pedestrian hybrid beacons as well. Table 4D-2 has been reproduced as Table 4-2. These principles can be challenging to balance in retrofit situations where optimal crosswalk locations may not be achievable. Note that there is also a potential concern over having a variety of crosswalk configurations (distance, orientation, etc.) used at the same type of intersection (roundabout or signal) or within the same community, although there is no research at the time of this writing to confirm this. Design Speed (mph) Brake Reaction Distance (ft) Braking Distance on Level (ft) Stopping Sight Distance (calculated) (ft) Stopping Sight Distance (design) (ft) 15 55.1 21.6 76.7 80 20 73.5 38.4 111.9 115 25 91.9 60.0 151.9 155 30 110.3 86.4 196.7 200 35 128.6 117.6 246.2 250 40 147.0 153.6 300.6 305 45 165.4 194.4 359.8 360 Note: Based on brake reaction distance of 2.5 s and deceleration rate of 11.2 ft/s2. Table 4-1. Stopping sight distance on level roadways (Table 3-1, AASHTO, 2011). 85th-Percentile Speed Minimum Sight Distance 20 mph 175 feet 25 mph 215 feet 30 mph 270 feet 35 mph 325 feet 40 mph 390 feet 45 mph 460 feet 50 mph 540 feet 55 mph 625 feet 60 mph 715 feet Note: Distances in this table are derived from stopping sight distances plus an assumed queue length for shorter cycle lengths (60 to 75 seconds). Table 4-2. Minimum sight distance for signal visibility (Table 4D-2, MUTCD, 2009).
24 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook The following section presents the most common crossing alignment options and the advan- tages and disadvantages associated with each option. 4.1.1.1 Entry and Exit Crosswalks Equidistant from the Circulatory Roadway Figure 4-2 shows a straight crosswalk alignment cutting directly through the splitter island, and Figure 4-3 shows a similar crosswalk alignment but with an angle point within the splitter island (sometimes referred to as a chevron style crosswalk). In both cases, the entry and exit crosswalks are approximately the same distance from the circulatory roadway. The requirement that the slope of the wheelchair ramp is perpendicular to the edge of the street may influence the alignment of the crosswalk. This type of crosswalk is generally placed one car length (20 ft) back from the yield line, although more separation (two car lengths) between the crosswalk and yield line can be advantageous if signals or beacons are used. Figure 4-2 shows a crosswalk on a roundabout leg that is set back one car length from the yield line. The entry and exit are both two lanes. The crosswalk is straight, and passes through the splitter island but does not bend at the splitter island. Figure 4-2. Entry and exit crosswalks same distance from roundabout with straight alignments. Figure 4-3 shows a crosswalk on a roundabout leg that is set back one car length from the yield line. The entry and exit are both two lanes. The crosswalk bends at the splitter island, allowing the crosswalk to cross the entry and exit perpendicularly. Figure 4-3. Entry and exit crosswalks same distance from roundabout with angled alignment.
Design Principles for Pedestrian Access at Roundabouts 25 Advantages of straight crosswalks ⢠Generally meets driver and pedestrian expectations for roundabout crosswalks, ⢠Minimizes the potential for out-of-direction travel distance for pedestrians, and ⢠Vehicle speeds are generally low at crosswalks because of roundabout geometry. Disadvantages of straight crosswalks ⢠More likely for pedestrians to treat as one-stage crossing (pedestrians may continue without stopping). ⢠More difficult to establish visual separation between pedestrian signal displays and audible separation between APS units in the splitter island, and ⢠Difficult to build curb ramps that are accessible; ramp must meet gutter at a 90 degree angle. Advantages of angled crosswalks ⢠More likely that blind pedestrians will align correctly when crossing from the curb because the crosswalk is perpendicular to the traffic on the leg, and square to the gutter; ⢠May make it easier to separate pedestrian signal indications because they are not in line with one another; ⢠Potentially less likely for pedestrians to treat as one-stage crossing than a straight alignment; ⢠Generally meets driver and pedestrian expectations for roundabout crosswalks; ⢠Minimizes the potential for out-of-direction travel distance for pedestrians; and ⢠Vehicle speeds are generally low at crosswalks because of roundabout geometry. Disadvantages of angled crosswalks ⢠Angle point on splitter island cut-through needs to be substantial enough (i.e., raised) to be detectible (subtle changes in angle may not be detected by a blind pedestrians and they may not adjust their alignment for the second crossing). 4.1.1.2 Exit Crosswalk Farther from Circulatory Roadway Figure 4-4 shows a staggered crosswalk alignment with the exit crosswalk farther from the roundabout. This design is typically constrained by the location of the exit side crosswalk, which can benefit from more separation (40 ft) between the crosswalk and the yield line when Figure 4-4 shows a staggered crosswalk on a roundabout leg. The exit crosswalk is set back two car lengths from the roundabout, and the entry crosswalk is set back one car length from the roundabout (yield line). The entry and exit are both two lanes. The crosswalk has two 90-degree turns at the splitter island. Figure 4-4. Staggered crosswalk with exit crosswalk further from roundabout.
26 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook signal/beacon equipment is present. The pedestrian path within the raised splitter island needs to be clearly channelized to provide wayfinding guidance. The staggered design is contrary to common guidance for pedestrian mid-block crossings, which typically offset the crossing to the right. Offsetting the crossing from the splitter island to the right makes pedestrians naturally turn toward oncoming traffic and is believed to improve visibility. In the case of roundabouts, the offset to the left (in the direction of pedestrian travel) is deliberate as it achieves greater separation between the exit portion of the crosswalk and the circulating lane. The added benefits of increased driver reaction distance (especially for right-turning vehicles), the added queue storage, and the improved auditory information for blind pedestrians are believed to outweigh concerns that the design is different from a typical mid-block configuration. Figure 4-5 shows an example of this crosswalk placement option at a roundabout in Gatineau, Quebec. This photo is provided only for the purpose of showing an existing staggered crosswalk at a roundabout. Some design details, such as different crosswalk widths and island opening widths and the use of bollards as a buffer, are not desirable from an accessibility standpoint. Advantages of staggered crosswalks ⢠More vehicular storage space between the circulatory roadway and the exit crosswalk, ⢠Exiting drivers have more time to react to the crosswalk conditions, ⢠Right-turning vehicles from the upstream approach have additional time to react, and ⢠Motorist attention to the crosswalk may be improved as they can focus on the crosswalk after exiting the roundabout. Disadvantages of staggered crosswalks ⢠Higher vehicle speeds may result from locating the crosswalk further away from the central island and the circulatory roadway than usual (this is most commonly a challenge at exit crosswalks), Figure 4-5 is a photograph of the crosswalk placement option shown diagrammatically in Figure 4-4. This figure illustrates the signal placement and configuration of the splitter island in a real-world site in Canada. Other aspects of this crossing would not be deemed accessible by the guidance in this document. Potential problems include the lack of landscape separation to guide pedestrians to the crosswalk (bollards without fence are not sufficient), the lack of detectable warning surfaces at the curb and on the island, and the lack of audible information and APS in the pedestrian push-button. Figure 4-5. Staggered crosswalk with exit crosswalk further from roundabout in Canada.
Design Principles for Pedestrian Access at Roundabouts 27 ⢠Pedestrians are turned away from the flow of vehicular traffic that they will cross next as they negotiate the splitter island, and ⢠Pedestrians may benefit from channelization by fences or other treatments to discourage crossing at inappropriate locations. 4.1.2 Sidewalk Alignment At roundabouts where pedestrian access is provided, pedestrians are accommodated around the perimeter of the roundabout. Sidewalks are located outside of the circulatory roadway and crosswalks are located on the entry and exit legs. The speed-limiting geometry of roundabouts is a key element of safety for all modes, including pedestrians, which is not inherent in other intersection forms. The channelization of movements at roundabouts prevents many erratic vehicle maneuvers. Figures 4-6 and 4-7 show two examples of sidewalk placements at roundabouts. In both cases, a buffer is provided between the sidewalk and the roadway. The buffers help to: ⢠Direct pedestrians, especially those with vision impairments, to the crosswalks; ⢠Discourage the use of the central island by pedestrians; and ⢠Reduce conflicts between overhanging vehicles and pedestrians. Buffers should be a minimum of 2 ft wide and preferably 5 ft wide. If there is insufficient right- of-way for a buffer, fencing may be used. Sidewalks at roundabouts should be a minimum of 5 ft wide and preferably 6 ft wide. If the sidewalk is intended to be used as a multiuse path, as is Figure 4-6 shows a sidewalk that follows the curvature of the roadway in the roundabout but is separated by approximately a 4 ft to 5 ft wide landscaping buffer. Figure 4-6. Roundabout with landscape buffer following roadway curvature.
28 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook sometimes done at roundabouts, the sidewalk functions as a shared use path and the sidewalk should be a minimum of 10 ft wide. Where the sidewalk is routed entirely away from the corner, pedestrians are unlikely to cross from an unintended location. Pedestrians, including those with visual impairments, will be âchanneledâ directly to the crosswalk; and there is minimal opportunity for failure to find the crosswalk. The sidewalk can approach the crosswalk in a direction that is in line with the direc- tion of the crosswalk, which can also assist pedestrians who are blind with aligning to cross. Figure 4-8 shows a single-lane roundabout where this sidewalk location technique was used. The example also shows good use of landscaping and placement of detectable warnings on the curb side and the splitter island. The cut-through of the splitter island is further wide enough to compensate for errors in maintaining the crossing heading. 4.1.3 Buffering 4.1.3.1 Landscaping Grass or a landscaping strip at the outer edge of the sidewalk indicates to pedestrians who are blind that they are not intended to cross in that location. It also provides a surface that can be trailed with a long cane to locate the crosswalk. This treatment, shown in Figure 4-9, may also decrease the likelihood that other pedestrians will cross from unintended locations. Pedestrians who are blind are unlikely to cross to the central island of a roundabout if there is continuous grass or a landscaping strip that is interrupted only by a curb ramp at a crosswalk. Figure 4-7 shows a straight sidewalk on the outside quadrant of a roundabout. The buffer is several times wider and the overall footprint is larger than if the sidewalk curved to follow the alignment of the outside curb of the roundabout. Figure 4-7. Roundabout with straight sidewalk and wide landscape buffer.
Design Principles for Pedestrian Access at Roundabouts 29 At the roundabout corner visible in Figure 4-8, the sidewalk between the crosswalks on either side of the corner curves in the opposite direction from the curb line. This results in a very wide area of grass and other landscaping between the sidewalk and the curb of the circulatory roadway, making it unlikely that any pedestrian will be inclined to cross to the central island. A pedestrian who is traveling toward the roundabout from either approach will find that the grass strip along the curb line ends where the crosswalk begins to cross the street beside them. If they wish to cross the inter- secting street, the continuation of the sidewalk turns away from the roadway and curves around to lead them directly to, and in line with, the crosswalk for the intersecting street. As noted in the text, the splitter island cut-through is as wide as the crosswalk and there are low plants on the non-walking areas of the island. Figure 4-8. Sidewalk curving away from the corner to guide pedestrians directly to the crosswalks. Figure 4-9 shows a narrow landscaping strip of low plants between the wide sidewalk and the travel lanes at this two-lane roundabout. Landscaping is present on both sides of the curb ramp. Figure 4-9. Landscaping that discourages crossing to the central island and provides an edge that blind pedestrians can follow (i.e., trail) with the long cane to locate a curb ramp.
30 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook Such a landscaping strip could be gravel, grass, or some other surface that is detectable under foot. However, rough brick or a cobblestone type of surface between the sidewalk and the curb or on an island was often not recognized by participants in this research as a non-walking surface. Such a surface did not provide the desired cues to the crosswalk location or prevent crossing from the wrong location. An example is shown in Figure 4-10. A grass or landscaping strip where pedestrians are not intended to cross satisfies the PROWAG-NPRM requirement for separation between the sidewalk and the street (R306.3.1). If pedestrians who are blind choose to follow the edge of the grass or landscaping nearest the street, it will lead them to an opening at the crosswalk. However, if they are not actively using the technique of following (i.e., trailing) the grass or landscaping but are traveling in the center of the sidewalk or following the edge of the sidewalk on the side farthest from the street, they may fail to find the crosswalk. It is important that the landscaping is kept low enough so that it does not obstruct the driverâs view of pedestrians waiting to cross, especially pedestrians of short stature or who are traveling with the aid of a wheelchair. 4.1.3.2 Fencing and Bollards Fencing, shown in Figure 4-11, or bollards connected by chains where crossing is not intended, indicates to all pedestrians that they should not cross in locations so marked. Bol- lards alone are not sufficient indications to blind pedestrians that they are in a non-crossing location (unless they are less than approximately 24 in. apart) as they may pass through without encountering a bollard. When chains are used between bollards, the lower edge should be no higher than 15 in. above the sidewalk, as required by PROWAG-NPRM R306.3.1. Chains that are more than 15 in. above the sidewalk may not be detected by a user, because the long cane may slide under the chain without touching it. A higher chain should also be provided so it is readily visible to aid pedestrians who are not using a long cane in detecting it. Bollards and chains should contrast with surrounding surfaces so that they can be seen by travelers with reduced vision who do not use a long cane or dog guide. Figure 4-10 shows a roundabout approach with surface material that was not recognized as a non-walking surface by blind participants. The cobblestone surface was installed at this roundabout between the concrete paved side- walk and the curb, but it did not provide guidance (that might have been intended). The inset on the right shows the size of the cobblestones in comparison to a foot; each cobblestone is approximately the width of the foot, with an inch or more of grout between the stones. Figure 4-10. Example of surface material that was not recognized as a non-walking surface by blind participants.
Design Principles for Pedestrian Access at Roundabouts 31 Well-designed bollards connected by chains satisfy the PROWAG-NPRM requirement for separation between the sidewalk and the street (R306.3.1). 4.1.3.3 Central Island Treatments The central island of a roundabout is not to be used by pedestrians because access to it requires crossing the circulatory roadway. Design techniques to discourage pedestrians from using the central island include: ⢠Use of different materials for sidewalks and the truck apron and ⢠No placement of objects that would attract pedestrians to the central island. 4.1.4 Detectable Warning and Guidance Surfaces At crossing points on the curb and on splitter islands with no difference in level between the sidewalk curb line and the street, detectable warning surfaces are needed to alert blind pedestri- ans to the edge of the street (i.e., the street/sidewalk boundary). A detectable warning surface is a pattern of small truncated domes with specific size and location characteristics specified by ADA guidelines. It must be detectable under foot as well as with a long cane because people with low vision or dog guide users may not be using a long cane. They serve as a hazard warning for blind pedestrians (and may serve this function for other pedestrians). Detectable warning surfaces should be installed in pairs, like parentheses, one at the beginning of a crossing and one at the end. When detectable warnings surfaces are not provided at the edges of splitter islands, blind pedestrians will not know they have reached a refuge area. If a two-stage crossing is desirable, as is usually the case at roundabouts, detectable warn- ing surfaces are required on both ends of the crosswalks (within the splitter island and on the At the roundabout in Figure 4-11, a wide brick sidewalk is separated from the circular roadway by a 3 ft high metal fence that ends where the crosswalk begins. On the approach to the crosswalk leading up the street toward the roundabout, there is a wide grass strip terminating with a tall brick pillar at the beginning of the crosswalk. Both the grass and the fence can be trailed by a blind pedestrian using a long cane. Figure 4-11. Fencing and grass strip at a roundabout corner.
32 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook outside of the roundabout). On the splitter island, two separate detectable warnings are required to distinguish the entry and exit portions of the crossing. Each detectable warning surface needs to be 2 ft wide, with at least 2 ft of separation between the two sets of warning surfaces, resulting in an island width of at least 6 ft. The detectable warning surface must cover the entire curb ramp area that is level with the street in order to be reliably detected. As shown in Figure 4-12, a pedestrian can step past the detectable warning surfaces that do not extend across the entire width of the cut-through island and into the street without realizing it. Even though good landscaping at roundabouts and CTLs prevents pedestrians who are blind from crossing at an unintended location, if they are not trailing and looking for a break in the landscaping, they may fail to notice the break in the landscaping to the street side and the associ- ated curb ramp and crosswalk. It is not uncommon for pedestrians who are blind to miss curb ramp entries and continue walking around wide-radius corners characteristic at roundabouts and CTLs without realizing that they have done so. PROWAG-NPRM states that âEuropean and Australian roundabouts provide a 610 mm (24 in.) width of tactile surface treatment from the centerline of the curb ramp or blended transition across the full width of the sidewalk to provide an underfoot cue for identifying pedestrian street crossingsâ (Advisory R306.3.1). This tactile surface treatment referred to by the U.S. Access Board is a bar tile surface or guidance tile, as shown in Figure 4-13, which is used in Australia. A variation of the tile shown in Table 4-13, with bars perpendicular to the direction of the crosswalk, is shown in Figure 4-14, as both an indication of the location of the crosswalk and to provide alignment information to blind pedestrians. Bar tiles are optional treatment and are not subject to the same requirements as detectable warning surfaces. Figure 4-12 shows an example of a pedestrian stepping past an incorrect installation of a detectable warning surface at a roundabout crossing. The detectable warning surface does not cover the entire cut-through area at a splitter island, and the pedestrianâs left foot is just to the left of the detectable warning surface in the picture on the left. In the picture on the right, the pedestrian has taken a step and the right foot is past the detectable warning at the street edge. The pedestrian thus may not detect the edges of the island and may continue into the travel lanes. Figure 4-12. Example of incorrect detectable warning surface installation at a roundabout crossing.
Design Principles for Pedestrian Access at Roundabouts 33 Figure 4-13 shows an example of an Australian bar tile surface installed across a sidewalk to indicate the location of the crossing at the roundabout (outside of frame on the left). A person using a long cane is approaching the surface with the cane tip contacting the bar tile surface. The bar tile surface is 2 ft wide in the direction of pedestrian travel and extends across the entire width of the sidewalk. Bars are aligned with the direction of the crosswalk. Figure 4-13. Australian bar tile surface. Figure 4-14 shows an experimental bar tile application from the Raleigh pilot data collection, with bars perpendicu- lar to the crosswalk direction. The curb ramp, gutter, and detectable warning surface at this location are not aligned with the direction of travel at the crosswalk but the bar tile treatment is aligned with the direction of the crosswalk. The treatment is a temporary surface installed for research about the usefulness of bar tiles to provide an indication of the crosswalk location and alignment. Figure 4-14. Experimental bar tile with bars perpendicular to the direction of the crosswalk.
34 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook 4.1.5 Curb Ramps 4.1.5.1 Curb Ramp in Line with Crosswalk to Provide Alignment Cue While travelers who are blind are not usually able to align precisely with the running slope of a curb ramp, ramp slope does influence alignment (Scott et al., 2011a). Therefore when curb ramps slope in the same direction as travel on the crosswalk, alignment and subsequent crossing by pedestrians who are blind are likely to be more accurate. Pedestrians who are blind may also cue on the street gutter and align themselves so that they are perpendicular to the gutter or the curb line on each side of the ramp. They may be more likely to align correctly if the crosswalk is perpendicular to the gutter. In an optimal design for wayfinding by pedestrians who are blind, curb ramps slope in the direction of travel on the associated crosswalk. However, curb ramps must intersect the roadway and the roadway gutter as near to 90 degrees as possible to accommodate assistive devices such as wheelchairs, which may otherwise be unstable as they transition between the pedestrian and the vehicular way. In some designs and locations, that requirement may conflict with aligning the ramp slope with the direction of the crosswalk. At roundabouts, moving the location of the crosswalk away from the circulatory roadway may enable associated crosswalks to both intersect the roadway at 90 degrees and slope in the same direction as the crosswalk. 4.1.5.2 Returned Curb in Line with Crosswalk to Provide Alignment Cue Where a grass strip or landscaping is used at the sidewalk edge, a curb ramp having returned curbs that are parallel to the direction of the crosswalk can be used to assist pedestrians who are blind with aligning to cross. They may trace (i.e., take a line of direction) from the direction of a returned curb with a long cane or with the side of the foot. Figure 4-15 shows a roundabout with curb returns on the ramp. There is no need for flare on the sides of ramps that are bordered by grass or landscaping. Flares are only necessary to eliminate tripping hazards at locations where other pedestrians may walk across the ramp on the sidewalk. 4.1.5.3 Parallel Curb Ramps Parallel ramps are used in situations where sidewalks are narrow, not allowing for a compliant curb ramp perpendicular to the curb. This is quite common at CTLs and at some roundabouts. Note that when installed at roundabouts without landscape strips, as shown in Figure 4-16, they do not comply with PROWAG requirements for separation unless some type of fencing is installed. For a parallel ramp, the entire sidewalk is sloped down to the level landing at the crosswalk, and then slopes back up. For wheelchair users and individuals with mobility impair- ments this can be a disadvantage if they are continuing along the sidewalk, because they have to travel up and down ramps unnecessarily. For individuals who are blind, parallel ramps can be confusing in terms of detecting the slope and determining the correct direction of travel on the crosswalk. Detectable warning surfaces must be installed where the level landing meets the street to provide an indication of the edge of the street. An example of a parallel curb ramp is shown in Figure 4-16. The lack of landscape separation or fencing in the figure poses accessibility challenges. 4.1.6 Crosswalk Markings to Provide Cue to Maintain Travel Within the Crosswalk For pedestrians with low vision, marked crosswalks can provide useful cues to the crosswalk location and can assist with maintaining travel within the crosswalk. Pedestrians with low vision
Design Principles for Pedestrian Access at Roundabouts 35 Figure 4-15 shows a pedestrian waiting to cross an exit lane from the corner to the splitter island. On each side of the curb ramp is a sloping curb with vertical sides between the ramp and the grass, which is aligned with the direction of travel on the crosswalk. The cut-through in the splitter island is also bounded by returned curbs so that following the curbing all the way across the island could aid in maintaining crossing direction. There is grass on both sides of the ramp, which reduces the likelihood of pedestrians approaching the ramp from a less than optimal direction. Figure 4-15. Curb ramp with returned curbs. Figure 4-16 shows a parallel curb ramp at a roundabout crossing. A parallel ramp is often used when there is a narrow sidewalk at the back of curb. The entire sidewalk slopes down to a level landing at the crosswalk location. The detectable warning surface is installed along the curb line for the entire width of the level area. As noted in the text, there is no landscaping or barrier between the sidewalk and the curb, so a blind person is not guided to the crosswalk location. Figure 4-16. Parallel curb ramp.
36 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook have stated a preference for the ladder type crosswalk markings. Ladder markings have both trans- verse and longitudinal lines, making it easier for a person with low vision to follow a line across the crosswalk. The longitudinal lines make the crosswalk more visible to drivers. Crosswalks that are brick colored may not be distinguishable from the asphalt street color for individuals who are color blind, and are not as visible to drivers. An example of a ladder-style crosswalk marking is shown in Figure 4-17. 4.1.7 Island Design The principles of splitter island design are discussed in the Green Book and NCHRP Report 672. Splitter islands should be at least 6 ft or more wide where the crosswalk passes through, allowing storage for a person pushing a stroller, walking a bicycle, or using a wheelchair. Splitter islands are usually, but not always, raised above the surface of the roadway, with cut-throughs to the street level to accommodate wheelchair users. Where the crosswalk passes through the splitter island, it is preferred that the splitter island be cut so that pedestrians remain on the elevation of the road surface rather than passing up a ramp and then immediately down another; edges on the cut-through can also assist blind pedestrians with wayfinding. To distinguish the island surface to the left and right of the cut-through crosswalk from a sidewalk, the raised area of the island should be landscaped or have a gravel surface to clearly indicate that it is not an intended walking environment. Pedestrians who are blind or who have low vision need appropriate guidance through the island area to the other crosswalk or crosswalks from the island. A completely paved island with no landscaping materials present in areas adjacent to the crosswalk can be disorienting, as was observed at several sites studied in this research (Figure 4-18). In addition and as noted earlier, detectable warning surfaces must be provided at the boundary between the island and the street to alert individuals to the location of the street/island boundary. Paths across refuge islands are typically cut-through (level with street) or ramped. Some par- ticipants in this research expressed a preference for ramped pathways, so that they could detect more easily that they had reached the island with an upward slope as well as the detectable warn- ing surface. Even when detectable warning surfaces were installed correctly at cut-through and ramped refuge islands, some participants missed them. Figure 4-17 shows ladder crosswalk markings at a roundabout. Ladder markings have both transverse and longi- tudinal lines, with two lines on the outside edges of the crosswalk aligned with the direction of crossing and bars across between those two lines in the vehicle travel direction, making it easier for a person with low vision to follow a line across the crosswalk. The longitudinal lines make the crosswalk more visible to drivers. Figure 4-17. Ladder crosswalk marking.
Design Principles for Pedestrian Access at Roundabouts 37 Islands with ramps must be wide enough in the direction of pedestrian travel to allow for two curb ramps with a level landing area between the ramps. The minimum width then depends on the vertical elevation of the sloped ramp. Between the sloped ramps, at least a 4 ft2 landing needs to be provided. If the island is not wide enough to accomplish this, a cut-through island may be the only feasible alternative. A short ramp, raising the cut-through area by an inch or two, may provide some information to blind pedestrians and reduce water and debris from gathering in the cut-through area. Cut-through islands need to be at least 6 ft wide in the direction of pedestrian travel to allow for a 2 ft detectable warning at each road transition point, with a gap of at least 2 ft between sets of detectable warnings. The island opening also needs to be at least 5 ft wide in the direction of vehicle travel to allow two wheelchairs to pass one another (required by proposed PROWAG). Ideally, the island opening should be as wide as the crosswalk. These dimensions are illustrated in Figure 4-19 for a cut-through island, and in Figure 4-20 for an island with ramps. The area outside the prescribed path should also be detectable as a non-walking surface. At roundabouts, landscaping is commonly used on the splitter islands to serve this purpose. 4.1.8 Right-Turn Lanes Some roundabouts have right-turn lanes, which are generally designed in one of two ways: ⢠The lane is a bypass laneâseparated from other entry lanes with a raised islandâand does not yield to traffic in the circulatory roadway. Bypass lanes may yield to exiting traffic, have a merge area, or have a dedicated receiving lane. ⢠The lane is exclusively for right-turning vehicles, but enters the roundabout and yields to cir- culating traffic like other entry lanes do. There may or may not be painted separation between The blind pedestrian in Figure 4-18 is standing at the edge of the splitter island approximately 20 ft from the cross- walk at a roundabout island with a zig-zag crosswalk and a cut-through pedestrian channel. He has stepped up on the paved area out of the cut-through. A second person, who is an orientation and mobility specialist involved in the research, is walking toward him. The raised portion of the splitter island is not distinguishable from the unraised por- tion, as a result of which the island provided insufficient wayfinding information to the blind participant, who stepped up onto the island from the cut-through area and is preparing to cross the street outside the crosswalk area. Figure 4-18. All-paved roundabout splitter island.
38 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook Figure 4-20 shows a wider island than a cut-through (dimensions not given) with curb ramps sloping up on each side with detectable warning surfaces at the base of the ramps at each street edge. A 4 ft level landing between the ramps is shown. Figure 4-20. Minimum refuge island dimensions for an island with ramps. Figure 4-19 shows a 6 ft minimum width island with a cut-through pedestrian path. Within the cut-through area of the island for the full width of the cut-through is a 2 ft section of detectable warning surface, then 2 ft of smooth surface, and then another 2 ft section of detectable warning surface. Figure 4-19. Minimum refuge island dimensions for a cut-through island.
Design Principles for Pedestrian Access at Roundabouts 39 the lanes, but there is no pedestrian refuge. Two types of non-bypass right-turn lanes are shown in Figure 4-21. Right-turn bypass lanes at roundabouts present many of the same challenges for pedestrians as CTLs at signalized intersections. 4.2 Traffic Control Device Applications Three major types of traffic control devices are considered in this section: standard pedestrian signals, pedestrian hybrid beacons (PHBs), and rectangular rapid-flashing beacons (RRFBs). In general, all three devices may be used at roundabouts. In addition, this section discusses signing and marking at roundabouts, as well as other treatments including raised crosswalks. 4.2.1 Type of Traffic Control Device A standard pedestrian signal as defined in this section displays a red-yellow-green indica- tion to motorists (resting in green) and a walking personâupraised hand (resting in upraised hand) indication to pedestrians. A standard pedestrian signal can be implemented in the vicin- ity of roundabouts, provided that the signal is located far enough from the circulatory roadway Figure 4-21 shows two types of non-bypass right-turn lanes at roundabouts. Figure 4-21(a) shows a lane that is exclusively for right-turning vehicles, but enters the roundabout and yields to circulating traffic like other entry lanes do. Figure 4-21(b) shows a variation of this configuration, with additional gore striping to accommodate truck traf- fic. Neither is considered a bypass laneâwhich would have to be separated from other entry lanes with a raised island. Bypass lanes may yield to exiting traffic, have a merge area, or have a dedicated receiving lane. Figure 4-21. Types of non-bypass right-turn lanes at roundabouts. (a) (b)
40 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook to minimize potential confusion between the green indication and the yield sign at the entry to the roundabout. Current judgment suggests that a separation of 150 ft or more should be sufficient to minimize driver confusion, but further research is needed to confirm or refine this suggestion. A PHB displays a sequence to drivers and pedestrians as described in MUTCD, Chapter 4F. It requires a signal controller with a conflict monitor/malfunction management unit because of potentially conflicting vehicle and pedestrian displays. Hardwire connections to displays are needed to enable conflict monitor/malfunction management units to operate. In addi- tion, multiple controllers may be needed to operate a full and independently operated set of PHBs on all the entries and exits of a roundabout because of limitations in the numbers of rings available within a controllerâs software. Figure 4-22 shows a photograph of a PHB at a roundabout in Golden, Colorado, and Figure 4-23 shows the sequence of operation for the vehicular and pedestrian signal heads. Since this beacon provides a walk indication, a stan- dard APS can be used to provide information to pedestrians who are blind or to those who have low vision. The RRFB is significantly different from the standard pedestrian signal and the PHB in that it does not display either a red indication to the motorist or a walk indication to the pedestrian. Rather, it is a visually enhanced warning device that is activated by the pedestrian. Because of their differences in operation, an RRFB does not require a signal controller with a conflict monitor/ malfunction management unit because there are no pedestrian displays. However, in order to be usable by a pedestrian who is blind or who has low vision, an audible information device should be integrated into the pushbutton. This device does not provide a walk signal, but instead provides information about the functioning of the device, with a pushbutton locator tone to let a person who is blind know the device is there, and be able to find it easily. An audible message when the lights are flashing should state âyellow lights are flashingâ as recommended by MUTCD on its FAQ page. A vibrotactile indication, such as is provided by an APS, is not appropriate since that could be mistaken for a walk indication. Figure 4-24 shows an RRFB at a roundabout in Oakland County, Michigan. Figure 4-22 shows a vehicle stopped at a red indication at the crosswalk on a roundabout entry. The red indication is displayed on two side-by-side ball signals on top of the display. A sign on the signal post states âstop on red.â A pedestrian is crossing in the crosswalk. Figure 4-22. Pedestrian hybrid beacon at roundabout in Golden, Colorado.
Design Principles for Pedestrian Access at Roundabouts 41 Figure 4-23 shows the six intervals in a sequence for a PHB. Each interval is shown as a signal face having three lenses: two horizontally aligned with a third centered under them. The first interval is labeled â1 Blank for Drivers.â It shows two dark (black) signal faces with one dark signal face centered below them. Beside the interval is a pedestrian signal display with an orange hand symbol. An arrow points to the pedestrian display with the text information: âNote: 2009 MUTCD allows the option for the pedes- trian display to rest in dark at roundabouts. (Section 4F.03).â The second interval is labeled â2 Flashing Yellow.â It shows two dark signal faces above an illuminated circular yellow signal. Beside the interval is a pedestrian signal display showing an orange hand symbol. The third interval is labeled â3 Steady Yellow.â It shows two dark signal faces above an illuminated circular yellow signal. Beside the interval is a pedestrian signal display with an orange hand symbol. The fourth interval is labeled â4 Steady Red.â It shows two illuminated circular red signals on top with one dark signal face centered below them. Beside the interval is a pedestrian signal display with a walking person symbol, indicating walk. The fifth interval is labeled â5 Wig-Wag.â It shows two signals on top with one dark signal face centered below them. The right signal face of the top display is illuminated red. Beside that is a pedestrian signal display with an orange hand symbol. The sixth interval is labeled âReturn to 1.â It shows two dark (black) signal faces with one dark signal face centered below them. Beside the interval is a pedestrian signal display with an orange hand symbol. A note at the bottom of the graphic states: No green ball to cause possible confusion with the yield sign. Figure 4-23. Sequence of displays at a Pedestrian Hybrid Beacon. Note: No green ball to cause possible confusion with yield sign 4.2.2 Location of Vehicle Signal/Beacon Faces MUTCD, Section 4D.12, governs the visibility, aiming, and shielding of signal faces, with guid- ance on the minimum sight distance. The design speeds (based on the fastest path radii of a roundabout per NCHRP Report 672) should be used to determine the minimum sight distances required. In addition, at least one and preferably two signal/beacon faces shall meet the lateral positioning requirements of MUTCD, Section 4D.13. At roundabouts, this can be more challenging on the exit side, given the relatively close proximity of a typical crosswalk to the circulatory roadway and to vehicles that may be coming as right turns from the upstream entry. The traffic control device needs to be sufficiently visible to both sources of upstream traffic.
42 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook Furthermore, the use of overhead signals can also influence placement. A driverâs visibility of an overhead signal can be restricted by the roof of a vehicle if the vehicle is less than 40 ft from the stop line associated with the signal. Beacons can be mounted on poles along the side of the roadway (side-mounted), placed over- head using a mast arm or span wire installation (overhead), or a combination of the two. As dis- cussed in Section 4D.13 of MUTCD, at least one and preferably both of the primary signal faces shall be within 20 degrees to the left or the right of the center of the approach, as measured from a point 10 ft prior to the stop bar. This section of MUTCD governs traditional green/yellow/red signals and also applies to PHBs. It is appropriate for other types of beacons (RRFBs, flashing beacons, etc.) to be located in this manner as well. Figure 4-25 shows the use of side-mounted Figure 4-24 shows a crosswalk on a roundabout entry with an RRFB. Arrows added to the photograph point to a light bar installed below the pedestrian warning sign, which is on a post beside the crosswalk, on the downstream side. This light bar is where the rapid flashing beacon lights are displayed. Figure 4-24. Rectangular rapid flash beacon at a roundabout in Oakland County, Michigan. Figure 4-25 shows the placement of side-mounted traffic signals or beacons on a roundabout leg. For both the entry and the exit, one pedestal-mounted signal is placed in the splitter island and one pedestal-mounted signal is placed immediately beyond the outside curb. Both signals and signal poles are on the downstream side of the crosswalk. The entry and the exit are both two lanes. Figure 4-25. Use of side-mounted vehicle displays only at roundabouts.
Design Principles for Pedestrian Access at Roundabouts 43 vehicle displays at a roundabout. Although not shown in the figure, a supplemental nearside signal head may also be beneficial. If overhead signals are used, the signal mounting height is governed in MUTCD, Sec- tion 4D.15. For overhead signals, the top of the face cannot exceed 25.6 ft over the roadway, and the bottom of the face cannot be below 15 ft over the roadway. For side-mounted sig- nals, the bottom of the signal shall be a minimum of 8 ft and a maximum of 19 ft above the sidewalk. The following mounting locations are recommended for crosswalks at roundabouts depend- ing on the number of travel lanes that the crosswalk is spanning: ⢠One-lane crossings: side-mounted vehicle displays ⢠Two-lane crossings: either side-mounted or overhead vehicle displays ⢠Three-lane crossings: overhead and side-mounted vehicle displays recommended for visibility to center lane 4.2.3 Location of Pedestrian Signal Faces and Accessible Pedestrian Signals Pedestrian signal face locations and APS are governed in MUTCD, Chapter 4E. Specific atten- tion should be paid to the location of APS units next to the crosswalk and in proximity to one another, especially within the splitter island. Refer to MUTCD, Sections 4E.08 to 4E.13, for further guidance on this topic. APS, as well as audible information devices that may be used with RRFBs, have a pushbutton locator tone to indicate to a blind pedestrian the existence of a pushbutton and to help them find it. The pushbutton locator tone is emitted from a speaker in the pushbutton housing and is supposed to be audible 6 ft to 12 ft from the button. Pushbutton locator tones repeat constantly at an interval of once per second. Other features of APS include a tactile arrow aligned with the direction of travel on the crosswalk, ambient sound response, and audible and vibrotactile walk indications. Audible information devices at RRFBs have a pushbutton locator tone and a speech message providing a message that âyellow lights are flashing.â If a crosswalk has a signal or beacon and APS or audible information devices are provided in the splitter island for a two-stage crossing, a wider splitter island is needed. The pushbuttons and audible messages must be separated by at least 10 ft, and poles must be set back from the curb by 2 ft to reduce the likelihood of being struck by vehicles and to properly locate pedestrian pushbuttons (see MUTCD, Sections 4D.16 and 4E.08 through 4E.10). Therefore, with a signal or beacon and a straight pedestrian crossing, the minimum recommended width of the splitter island at the crosswalk location is 14 ft. Moving the exit portion of the crosswalk further away from the roundabout in a zig-zag island design can aid with providing adequate space for the required separation of entry and exit traffic control devices for pedestrians. The zig-zag may also allow for an island that is less than 14 ft wide, while still providing adequate separation, as illustrated in Figure 4-26. This separation is required to place the pushbutton and the audible tone or message close to the crossing to which it applies and to prevent confusion between two crosswalks on the same corner or island. There is an exception in MUTCD 4E.08, paragraph 8, which allows push buttons to be placed closer, if speech walk messages are used. However, there has been no research on what the speech messages should say to clarify which leg of the roundabout the signal applies to. The designation, entry lane or exit lane, is not well understood by the general public, with a high likelihood of confusion for pedestrians who are blind if audible devices are
44 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook placed closer together. Although not specified by MUTCD, audible devices should be placed on the downstream side of the crosswalk (relative to the direction of vehicle travel) to avoid the audible message masking the sound of approaching vehicles. 4.2.4 Signing and Markings MUTCD, Section 3B.16, provides language on the placement of stop bars associated with crosswalks. MUTCD, Section 4D.14, indicates that signal faces shall not be less than 40 ft from the stop bar âexcept where the width of the intersecting roadway or other conditions makes it physically impractical.â If signal faces for a signalized crosswalk on a roundabout exit are less than 40 ft from the roundabout, it would be physically impractical to place the stop bar 40 ft or more from the signal face because it would be within the circulatory roadway. The crosswalk design should account for where vehicles will queue based on the location of the stop bar when determining the crosswalk location. High visibility crosswalk markings (also referred to sometimes as âzebraâ markings, in contrast to having two transverse lines on either side of the crosswalk) may make drivers more aware of the pedestrian crosswalk and provide guidance to pedestrians with low vision about the crossing location. On the other hand, transverse lines can help low vision travelers maintain their straight Figure 4-26 shows proposed locations of APS or audible information devices with push button, audible message and locator tones at a two-lane roundabout. Pushbuttons and devices for entry and exit are located downstream of the crosswalk, which separates the sound of the devices from that of approaching vehicles. On the splitter island, it also provides maximum separation between the two components of the crossing. Note that no vehicular signal heads are shown in the image. Figure 4-26. Location of pedestrian pushbuttons for zig-zag crossings.
Design Principles for Pedestrian Access at Roundabouts 45 line of travel while crossing (as noted in the section on wayfinding). As a result, a âladderâ type crosswalk (see figure 4-17), featuring both transverse lines and zebra stripes (or continental style markings), may be the most effective crosswalk marking to assure access to blind travelers and travelers with low vision, although research on the effect of the different markings is limited. An in-road sign reminding drivers that it is a state law to yield to pedestrians within the cross- walk (Figure 4-27) may increase yielding behavior. Research at non-roundabout locations has shown that these signs are effective in increasing the yielding behavior of drivers (Fitzpatrick et al., 2006) and they have been used effectively at some roundabout installations. The sign, yield here to pedestrians, in Figure 4-28, is intended to be used in conjunction with an advance yield line to encourage drivers to stop further from the crosswalk. However, vehicles stopping further from the crosswalk may make it harder for blind pedestrians to detect the vehicle that has yielded and may lead to unexpected conflicts. However, having a sign clearly indicating to drivers where they are intended to yield presumably enhances the predictability of where to listen for yields. 4.2.5 Other Treatments Numerous treatments are intended to increase pedestrian visibility and encourage drivers to yield to pedestrians. They can range from typical warning signs and crosswalk markings to pedestrian-actuated flashing beacons. Higher yielding rates may result in more opportunities Figure 4-27 shows two examples of in-road signs reminding drivers of the state law to either yield or stop for pedes trians within the crosswalk. Near the top of each sign are the words âstate law.â Figure 4-27(a) includes a small yield sign, the word âto,â and the pedestrian symbol with the words âwithin crosswalkâ below the pedestrian symbol. Figure 4-27(b) includes a small stop sign, the word âforâ and the pedestrian symbol with the words âwithin crosswalkâ below the pedestrian symbol. The yield and stop signs are listed in MUTCD as numbers R1-6 and R1-6a, respectively. R1-6 R1-6a (a) (b) Figure 4-27. In-road pedestrian signs.
46 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook for crossing for pedestrians who are blind or who have low vision. However, as noted above, the pedestrian has to be able to detect that a vehicle has yielded, the driver has to wait long enough for the pedestrian to make that decision, and the pedestrian has to be willing to cross in front of a yielding vehicle. At multilane crossings, the second lane has the potential for multiple threat events and is a big concern for pedestrians who are unable to visually ascertain the status of the second lane before crossing. Non-signalized treatments can be considered to improve the accessibility of crosswalks at roundabouts. Treatments that provide vertical deflection and thus reduce speeds such as raised crosswalks and speed humps, may improve the likelihood of drivers yielding to pedestrians. Testing of a raised crosswalk at a multilane roundabout is reported in NCHRP Report 674 and showed beneficial results in terms of the pedestrian level of risk and driver yielding. Evaluations in NCHRP Project 03-78B further found that raised crosswalks can help reduce vehicle speeds, increase driver yielding, and reduce pedestrian risk and delay. The potential impact of a raised crosswalk at roundabouts on the slowing down of vehicles needs to be considered before instal- lation. Further testing is needed to understand the range of conditions under which a raised crosswalk may be effective. At roundabouts, it may be possible to keep raised crosswalks closer to the circulatory roadway compared to a signal as discussed above. This tends to reduce out-of-direction travel for pedes- trians. Detectable warnings are essential to help a blind pedestrians identify the street or sidewalk boundary. Figure 4-29 shows a raised crosswalk at a two-lane roundabout. Design considerations for raised crosswalks specific to roundabouts have not been developed. Generally, a raised crosswalk refers to the crosswalk walking surface being elevated relative to the vehicular travel lanes across the entire width of the crosswalk (as opposed to a more narrow speed hump or bump). The key design dimension of the raised crosswalk are the vertical eleva- tion (typically between 3 in. and 5 in. higher than travel lanes) and the transition slope (typically between 1:10 to 1:15). In general, a higher vertical difference and a steeper transition slope will result in a slower design speed for vehicles. Figure 4-28 shows two examples of roadside signs indicating to drivers where to yield to pedestrians. Figure 4-28(a) is square and Figure 4-28 is rectangular. Within the black and white sign is a red yield sign, the word âhere,â a downward pointing arrow, the word âto,â and a pedestrian symbol or the word âpedestrians.â The square and rectangular signs are listed in MUTCD as numbers R1-5 and R1-5a, respectively. R1-5 R1-5a (a) (b) Figure 4-28. Sign for yielding to pedestrians.
Design Principles for Pedestrian Access at Roundabouts 47 It is further possible to combine a flashing beacon or RRFB with a raised crosswalk. The beacons are primarily intended to increase driver awareness of the crosswalk, alert them of the presence of a pedestrian, and encourage drivers to yield. A raised crosswalk can be effec- tive in supplementing these treatments, by reducing vehicle speeds at the crosswalk, which can help reduce sight distance requirements, improve yielding, and reduce risk. Care is needed in ensuring an appropriate set of signs and pavement markings to accompany the combined treatments. Figure 4-29 shows an installation of a raised pedestrian crosswalk at the entry leg of a two-lane roundabout in Golden, Colorado. This location was studied as part of NCHRP Report 674. Figure 4-29. Raised crosswalk at a two-lane roundabout.
