Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 117


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 116
116 PART 3 Detailed Single-Lane Roundabout: North Carolina Introduction Several members of the research team are also involved in a separate research effort under sponsorship of the NIH. In This section describes detailed analysis results of data col- this multi-year NIH project, research on the general crossing lected at two single-lane roundabouts in North Carolina. The performance of blind pedestrians is performed, and a subset analysis and comparison of these two sites were previously of studies focuses on roundabouts. In particular, a study in published in Schroeder, Rouphail, and Hughes (2009), although the fall of 2004 investigated the feasibility of an automated the present document shows some revised variable definitions yield-detection system (AYDS) at a single lane roundabout at compared to the published paper. The first roundabout is Pullen Road and Stinson Drive in Raleigh (Site PS-RAL). The located at the intersection of 9th Street and Davidson Avenue data collection protocol at the PS-RAL study was comparable in Charlotte. This roundabout was included in the original data to DAV-CLT and included trials in both conditions with the collection scope of NCHRP Project 3-78A and was initially AYDS treatment "on" and "off." In this document, the PS-RAL proposed to be evaluated in a pre and post experiment with trials conducted in the "off" condition are compared to the data treatment installation. However, the treatment installation in the "before" study at DAV-CLT. and post study were aborted later in the project and funds In the data collection at DAV-CLT, data from a total of reallocated to other purposes. One of the uses of these funds was 10 blind subjects were analyzed. The dataset for PS-RAL the evaluation of the second single-lane roundabout described resulted in usable data from 12 blind participants as well as in this document. The roundabout at the intersection of Pullen six sighted comparison subjects (not shown). At both sites, Road and Stinson Drive in Raleigh was previously studied a full crossing consisted of four lane crossings (for example in a related project, using the same experimental protocol entryexitexitentry) with the starting order of lanes random- applied in NCHRP Project 3-78A. The analysis presented ized for each subject. At DAV-CLT each subject completed in this document was performed from video observations three full crossings at the northern and three full crossings of that study. Another use of the funds was data collection at at the southern crosswalk, resulting in a total of 12 entry and a single-lane roundabout in Golden, which is discussed in a 12 exit individual lane crossings. At the PS-RAL site each separate document. subject completed eight full trials at one crosswalk, resulting The original data collection scope for NCHRP Project 3-78A in 16 entry and 16 exit lane crossings. included the evaluation of one single-lane roundabout at the intersection of 9th Street and Davidson Avenue in Charlotte (Site DAV-CLT). In the discussion at the interim NCHRP North Carolina Single-Lane Project 3-78A panel meeting in January 2008 in Washington, Analysis Results D.C., concerns were raised that the low traffic volumes at this Site Description site were not representative of a typical single-lane U.S. round- about. As a result, the site was deemed to be accessible and The DAV-CLT roundabout has an inscribed diameter of would not substantively benefit from the installation of the approximately 140 ft and approach speed limits of 25 mph. proposed treatments. The NCHRP Project 3-78A team thus The PS-RBT has a smaller inscribed diameter of 88 ft and agreed to compare the crossing performance statistics to a also has approach speed limits of 25 mph. Exhibit 24 below higher-volume single-lane roundabout and contrast the acces- shows aerial views of both sites. The tested crosswalks are sibility criteria, which is the focus of this document. highlighted.

OCR for page 116
117 Exhibit 24. Aerial views of DAV-CLT and PS-RAL roundabouts. a) DAV-CLT b) PS-RAL When traffic volumes are compared, the major approaches experimental trials, which were carried out more often slightly on Davidson Avenue and Pullen Road have AADTs of about outside the peak hours, was relatively low. 9,900 and 15,000, respectively. The side streets on 9th Street The research team also gathered sample speed observations and Stinson Drive respectively have much lower volumes. at both sites. The approach speeds on the entry approach Exhibit 25 shows the peak hour entering volumes for both sites. lanes to the north and south crosswalk at the DAV-CLT site The data suggest that the a.m. and p.m. peak hour vol- were 27.6 and 26.0 mph, respectively. Upon entry, the aver- umes at the PS-RAL are about 50% and 90% higher than at age vehicle speed dropped to approximately 17.6 mph due to the DAV-CLT site, respectively. More importantly, the lunch the roundabout geometry. The average approach speed at the peak hour at PS-RAL has 240% more traffic, which is mostly southern crosswalk of the PS-RAL roundabout was lower than a result of generally low daytime volumes at the DAV-CLT at DAV-CLT at 22.8 mph. The average entering speed to the site. A similar trend was observed during the actual experi- PS-RAL roundabout was 15.6 mph. The average exiting speeds mental trials. While the DAV-CLT has medium traffic vol- at DAV-CLT and PS-RAL were approximately 17.3 and umes in the a.m. and p.m. peak hours, traffic during the actual 15.3 mph, respectively. The lower speeds at PS-RAL are likely Exhibit 25. Peak hour entering volumes for sites. a) PS-RAL Peak Hour Volumes Total Entering Volumes, Sep-2007 PS-RAL North East South West TOTAL AM Peak (7:30-8:30AM) 779 3 461 36 1279 Lunch Peak (12:15-1:15PM) 583 38 560 113 1294 PM Peak (5:00-6:00PM) 454 20 887 123 1484 b) DAV-CLT Peak Hour Volumes Total Entering Volumes, Nov-2007 DAV-CLT North East South West TOTAL AM Peak (7:30-8:30AM) 157 79 506 92 834 Lunch Peak (1:00-2:00PM) 198 26 272 39 535 PM Peak (5:00-6:00PM) 364 70 277 76 787