Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook (2017) / Chapter Skim
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From page 21... ...
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.
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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.
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Design Principles for Pedestrian Access at Roundabouts 23 • For crosswalks with traffic control device, minimum stopping sight distance needs to be provided. MUTCD specifies a minimum sight distance for the visibility of traffic signal heads in Table 4D-2.
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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 advantages 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)
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From page 25... ...
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)
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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.
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From page 27... ...
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.
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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.
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From page 29... ...
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.
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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.
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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)
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32 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook outside of the roundabout)
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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)
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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)
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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.
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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 transverse and longitudinal lines, making it easier for a person with low vision to follow a line across the crosswalk.
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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.
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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.
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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.
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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.
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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.
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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 driver's 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.
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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.
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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)
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Design Principles for Pedestrian Access at Roundabouts 45 line of travel while crossing (as noted in the section on wayfinding)
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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.
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From page 47... ...
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.
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