Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 93


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 92
92 courtesy, and yielding to pedestrians who identify themselves as the accessibility of crossings at CTLs, single-lane roundabouts, having vision impairment, by either carrying a long white cane and two-lane roundabouts for pedestrians who are blind. or by walking with a guide dog. The net benefit of increased driver yielding behavior is hypothesized to be greatest when Channelized Turn Lanes traffic volumes are high since the occurrence of crossable gaps and all-quiet periods decreases. The fact that high yield com- There is anecdotal evidence that a crosswalk located in pliance can result in low delays even under high volumes is the middle of the turn lane is preferable to a crosswalk at the made evident through the data from the PS-RAL single-lane upstream or downstream portion of the turn lane. The middle roundabout, although it may also be associated with a safety crosswalk establishes a short crossing path roughly perpendi- trade-off. Despite a high AADT and heavy peak-hour flows, cular to the trajectory of turning vehicles (and therefore is pedestrian delays were less than at the low-volume DAV-CLT useful for establishing alignment), and it physically separates roundabout. The difference is most likely attributable to a the conflict of turning drivers and pedestrians with the down- higher willingness of drivers to yield at the PS-RAL site. In stream merge point. Based on turning radii and associated this case, however, the PS-RAL site remained inaccessible to design speeds, this is also likely to be the location where speeds pedestrians due to a high rate of interventions. of right-turning vehicles are lowest. Since no alternate cross- In evaluating yielding behavior, two other considerations walk locations were tested at the CTL (i.e., upstream or down- are important. First, the length of time a driver is willing to stream), it is unclear from this research whether a different yield (i.e., driver patience) likely affects the ability of the pedes- crosswalk location would have any (positive or negative) impact trian to utilize that yield. The detailed study results shown in on the crossing ability of blind pedestrians. Appendix A show that most participants required several Field tests suggested that high vehicle speeds contributed seconds before crossing in front of a yielding vehicle, and some to the high incidence of unsafe crossings at the tested CTL; waited 10 s or more. Therefore, a yield that only lasts for a few therefore, geometric designs and treatments intended to reduce seconds is unlikely to result in a utilized crossing opportunity vehicular speed, such as traffic-calming designs, raised cross- for blind pedestrians. Second, the physical location of yields walks, pork-chop island design, narrow CTL width, small curve relative to the crosswalk is believed to affect the pedestrians' radii, and the absence of an acceleration lane may decrease ability to detect these events. It is believed that the observed the likelihood of unsafe crossing judgment by pedestrians who posttest increase in yield utilization at the two-lane round- are blind. However, none of these treatments were tested in about for both treatments is at least partly attributed to the fact this research. Support for low turning-vehicle design speeds for that drivers tended to yield closer to the crosswalk and there- CTLs is also given in the AASHTO Guide for the Planning, fore the rate of deceleration was more rapid. In other words, Design, and Operation of Pedestrian Facilities (2004). CTL it seemed easier to detect a vehicle that quickly decelerated to designs with raised crosswalk have been observed in several a stop close to the crosswalk than one that slowly coasted to a cities across the United States. stop farther from the crosswalk. No CTLs with acceleration lanes were studied in this Interestingly, two data collection sites with different traffic research, but based on anecdotal evidence it is expected conditions were located in Charlotte. At the tested single-lane that they may further increase speeds and may result in low roundabout, volumes were low and participants were delayed compliance with crosswalk laws and installed treatments. despite ample gap crossing opportunities as many waited for Dual-lane CTLs are included in the draft PROWAG as all-quiet periods. At the two CTL crossings, traffic volumes facilities where a pedestrian-actuated and APS-equipped signal were much higher and the delay was exacerbated by a very meets the accessibility requirements. While no dual-lane CTLs high level of ambient noise from the main intersection. All were part of this research, the crossing challenges observed at three crossing locations were characterized by a low propen- the tested single-lane CTL suggest that dual-lane CTLs may sity of drivers to yield, which may be characteristic of the local in fact be very challenging places to cross for a pedestrian who driving culture or may be coincidence. is blind. With two lanes, the expected challenges are related to higher volumes, higher speeds, and a risk of multiple-threat situations, compared to single-lane CTLs. Implications for Facility Design Detectable warnings complying with the draft PROWAG This section on implications for facility design is intended to are required at both curb and island ends of crosswalks to warn advance the discussion in this area and to direct future research. pedestrians who are blind that they are leaving the pedestrian The points below are based on field results from this and other way and entering the vehicular way. studies as well as anecdotal evidence that evolved from observ- A potential treatment that facilitates the auditory discrim- ing many crossing attempts by blind travelers at different loca- ination of right-turning (conflicting) and through traffic tions. Taken together, they comprise a toolbox for increasing should be considered and studied further. The sound strips