Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook (2017) / Chapter Skim
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Pages 78-97
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From page 78... ...
78 C H A P T E R 7 7.1 Assessment of Pedestrians Crossing at Roundabouts and Channelized Turn Lanes This chapter provides a method for the assessment of a pedestrian crossing at a roundabout or intersection with CTLs. The method is divided into thirteen principal steps geared at quantifying the performance of a given site.
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Crossing Assessment 79 The second performance check, pedestrian delay, is one commonly used by transportation analysts to evaluate the level and quality of service of pedestrian facilities for sighted pedestrians. In the context of this method, the delay is focused on the expected experience of a pedestrian who is blind.
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80 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook the decision of what LOS is acceptable is an agency decision. In other words, the performance target for pedestrian LOS is an agency policy decision.
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Crossing Assessment 81 in an area, where such treatments are used routinely at other intersection forms. In short, locally observed accessibility performance data is likely to be more accurate and representative of the "true" accessibility of a site in question.
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82 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook Figure 7-1. Methodology flow chart.
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Crossing Assessment 83 for design adjustments and treatment provision as needed. Key design elements needed for the crossing assessment include the number of lanes, lane widths, crosswalk location, treatment details, and design radii for the intersection itself.
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84 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook 7.3.2 Step 2. Predict Vehicle Speed at Crosswalk Vehicular speed has been identified as a key measure affecting pedestrian accessibility.
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Crossing Assessment 85 have an opportunity to accelerate leaving the roundabout, their actual speeds at the crosswalk are expected to be higher than those predicted by the respective controlling radii. As such, the speed is estimated at the fastest path radii, adjusted by the acceleration of vehicles as described in NCHRP Report 672.
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86 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook obstructions are also expected to impact the audible environment at the crosswalk and the ability to hear approaching vehicles without sound obstructions or deflections. The methodology developed to determine crossing sight distance adequacy at a roundabout or CTL has been adapted from the sight distance performance checks for vehicles at roundabouts from NCHRP Report 672, calculations and definitions from the Green Book, and the pedestrian mode methodology in Chapter 19 of the Highway Capacity Manual 2010.
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Crossing Assessment 87 uses the controlling radius for the particular movement from radii R2, R4, and R5 depending on whether the conflicting movement is a right-turning, through, or left-turning vehicle. For all exit-leg movements, the actual speed is adjusted to account for the vehicle's ability to accelerate before reaching the crosswalk as shown in Table 7-2.
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Figure 7-4. Pedestrian sight triangles for each crossing location.
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Crossing Assessment 89 the resulting sight "triangles" drawn relative from the respective waiting positions (on both curb and island) for a pedestrian to the end of the measured sight distance.
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90 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook Equation 7-5. Pedestrian critical headway from the Highway Capacity Manual, Chapter 19.
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Crossing Assessment 91 Equation 7-6. Estimating probability of yielding.
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92 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook analysts are encouraged to use local data or estimates should those be available. It is also noted that the relatively high gap utilization of 82.3% at two-lane entries compared to other locations may be biased by the specific sites studied in the research.
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Crossing Assessment 93 accelerating away from the roundabout)
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94 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook The quantity increases with a decreasing probability of crossing, P(Cross) , which in turn decreases with reduced availability and utilization of gaps and yields.
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Crossing Assessment 95 video observations. These risk assessment factors are correlated to the characteristics of the studied crosswalk to arrive at a risk prediction model.
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96 Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities: A Guidebook An underlying consideration of whether traffic control devices are understood by drivers and pedestrians also plays into the question of visibility. The key difference between visibility and sight distance (discussed in the another step of the crossing assessment method)
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From page 97... ...
Crossing Assessment 97 the signal display (without having to lean forward in their seat)
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