Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 16


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 15
15 vehicles, the blind pedestrian must wait until traffic is stopped the two traffic streams typically move perpendicularly to each or until there is no traffic approaching from either direction on other, presumably making it easier for someone who is blind the through street. to interpret directional traffic movements. Finally, the contin- The downstream crosswalk location creates different issues. uous flow of traffic circulating the roundabout can create a At the downstream location, drivers of vehicles in the turn lane difficult auditory environment, and the listening task is com- are more likely to be looking to their left at vehicles approach- plicated by elevated levels of ambient noise. ing on the major street and not to their right where a pedes- All of these factors may contribute to accessibility challenges trian may be waiting to cross from the curb. Where volumes at roundabouts and CTLs. Research in this area and the work on the major street are low and gaps required to merge from of this project have divided the crossing task into four princi- the turn lane are readily perceived, vehicles may accelerate pal areas that guide the understanding of the challenges faced as they approach the downstream exit, lessening the likeli- by pedestrians who are blind. Additionally, the four areas hood that they will yield to pedestrians. However, where vol- require different treatments to improve targeted aspects of umes on the downstream departure leg are high, there may pedestrian accessibility. The four crossing components are: be times in the signal cycle when vehicles in the channelized lane are regularly stopped to wait for a gap in traffic. Sighted 1. Locating the crosswalk, pedestrians often cross between stopped vehicles at these times, 2. Aligning to cross, but blind pedestrians may have difficulty determining that 3. Identifying a crossing opportunity, and vehicles have stopped. Higher speeds and lower likelihoods 4. Maintaining alignment during crossing. of yielding to pedestrians are also more likely when an accel- eration lane is provided at the CTL exit. In the following, each component is discussed in detail. Facilities built since 2001 compliant with the American with Disabilities Act (ADA) include a curb ramp with trun- Locating the Crosswalk cated-dome detectable warnings that delineate the edge of the roadway. If the crosswalk and ramp are located upstream A pedestrian approaching an intersection needs to be able to or downstream within the CTL, the ramp may terminate identify the location of the crosswalk. For standard orthogonal into the radius of the curve, which is not perpendicular to the intersections, this is a fairly simple task since the curb ramps crosswalk. Blind pedestrians may experience problems with are located in the vicinity of the corner of the intersection, usu- identifying the crossing location and alignment at all cross- ally within 15 ft if the turning radius is not significant. How- walks at channelized turn lanes because of the curvature. ever, at roundabouts and CTLs, there is no distinct point of interest (such as the corner) where a pedestrian would expect a crosswalk to be located. Instead, the auditory environment Accessibility Challenges from nonlinear traffic patterns can be difficult to navigate com- Recent research on the crossing performance of people who pared to the typical orthogonal intersection. are blind at complex intersections demonstrates that there are For roundabouts, finding the crosswalk is highly depend- unique challenges for this population (Ashmead et al. 2005, ent on the direction of travel and the side of the roundabout Guth et al. 2005). Complex intersections, including round- being approached. For instance, a pedestrian wishing to turn abouts and channelized turn lanes, present some unique chal- left with traffic approaching the roundabout from behind her lenges for pedestrians with vision impairments. The traffic would have the crosswalk on her left, similar to a standard control strategy at a roundabout entry leg is typically a yield orthogonal intersection. Even so, the circulating traffic does sign, and many drivers are able to enter the circle without the not provide a consistent point of reference to begin looking requirement to come to a full stop. Similarly, traffic exiting for the crossing location. The task of walking straight through the roundabout is free-flowing (often accelerating), resulting a roundabout intersection poses further challenges. The pedes- in largely uninterrupted traffic flow at the exit portion of the trian must be aware that she must navigate around the circle crosswalk. Traffic patterns at CTLs are similar in that the right- via sidewalk cues or landscaping and then locate the crossing turning movement is largely free-flowing. Crosswalks at both location a significant distance from where the typical crossing types of facilities are typically not signalized, and the task of would be located at a standard intersection. Since vehicles do identifying crossing opportunities is thus unassisted. Depend- not move in a perpendicular fashion with other vehicles, the ing on the geometric design and the location of the crosswalk, pedestrian may need repeated attempts to identify the crossing vehicle speeds may be relatively high, and the auditory inter- location, which can be time-consuming and dangerous. pretation is complicated because vehicles are moving on a cir- For similar reasons, CTLs can be challenging to a blind cular path (Ashmead et al. 2005). At signalized intersections, pedestrian. The unusual geometry associated with the large