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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.
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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
