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 136
136
Exhibit 59. O&M interventions for PHB crosswalk.
O&M Interventions PHB Crosswalk
Pre Frequency # of Crossings Percent
Entry 5 144 3.5%
Exit 2 144 1.4%
Overall 7 288 2.4%
Post
Entry 0 104 0.0%
Exit 0 104 0.0%
Overall 0 208 0.0%
40 crossings (for example two crossings a day over 4 weeks to the signal phases is intended to capture driver understand-
with 5 working days per week). However, given that inter- ing of and compliance with the signal indication. Second, the
ventions are very rare events, it is unlikely that the post inter- impact of the PHB installation on pedestrian-induced vehicle
vention is an absolute zero, but rather is small enough to where queues at the crosswalk is examined.
it was not measurable at the given sample size. Driver understanding of and compliance with the PHB can
Exhibit 60 explores the distribution of interventions by sub- be evaluated by relating the driver stopping behavior to the
ject and by time of day. Subjects who didn't return for the post indicated signal phase. Exhibit 61 shows a summary of 426 vehi-
experiment are shown with negative intervention rates to dis- cle events that were observed during and just after the trial as a
tinguish them from participants with zero interventions. The function of PHB signal phase. The exhibit shows the number
intervention rates show no trend by time of day. The figure of drivers who yielded (rolling or stopped yield) in each of
makes evident that several participants didn't experience any five signal phases: "Blank," "Flashing Yellow," "Solid Yellow,"
interventions even in the before case at the given sample size "Solid Red," and "Flashing Red." It then relates all vehicle
of 16 lane crossings. Given the rare nature of the intervention events to the phase that was active when the vehicle crossed
measure, a zero rate should not be interpreted as a perfectly the plane of the crosswalk. The exhibit further contains a
safe crossing. record of all vehicles that did not yield.
The results in Exhibit 61 show that many drivers who
encountered a pedestrian at a crosswalk yielded even before
Driver Behavior at the PHB
the signal was activated, while others didn't stop at all, even
In the evaluation of the PHB, an important question of when the signal was in the solid red phase. The events include
interest to traffic engineers is the effect of the signal on vehicle all drivers who in some way interacted with the PHB signal or
traffic flow. The driver behavior analysis described herein has the pedestrian. The exhibit does not include any events that
two main components. First, the behavior of drivers relative occurred before the signal was activated or after the trial was
completed. Exhibit 62 plots two categories of driver behavior
for each signal phase: (1) vehicles stopped or stopping, and
Exhibit 60. O&M interventions by subject and by (2) vehicles proceeding through the crosswalk.
time of day.
The exhibit shows that 34.1% proceeded through the cross-
PHB walk in "Flashing Yellow," which is permitted behavior. As the
20.0%
signal changes to solid yellow, still 11.4% of drivers proceed
PRE
through the crosswalk, which is allowable if the vehicles were
15.0% too close to the crosswalk to come to a stop. However, even dur-
POST
O&M Interventions
ing the "Solid Red," 12.6% of observed vehicles proceeded
10.0% through the crosswalk. This figure is a concern, since drivers are
legally required to stop for the red signal indication and because
5.0% pedestrians expected a crossing opportunity. Driver behavior
during "Flashing Red" shows that almost half of the drivers
0.0% (48.2%) remained stopped, suggesting some inefficiency in
1 3 6 9 11 16 4 7 10 12 14 17 2 5 8 13 15 18 driver behavior in response to the PHB.
-5.0% The second part of the analysis focuses on the impact of the
9:00am 11:30am 3:30pm
PHB installation on vehicle queues. Exhibit 63 shows the sta-
Subject tistics for the maximum vehicle queue lengths in the pre and
OCR for page 137
137
Exhibit 61. Vehicle events by yielding and stopping phases at PHB.
Yielding Vehicles and Phase Yielding Is Initiated Non-
Yielding
Signal Phase Blank Flash Y Solid Y Solid R Flash R TOTAL Vehicles
Crossing Phase
Flash Yellow 3 2 5 39
Solid Yellow 3 2 0 5 15
Solid Red 6 3 4 0 13 15
Flash Red 20 20 31 15 15 101 72
Blank 13 18 41 36 53 161 n/a
TOTAL 45 45 76 51 68 285 141
Total Vehicle Events 426
Exhibit 62. Evaluation of driver behavior at PHB.
100%
11.4% 12.6%
90%
34.1%
80% Proceeding
51.8% through
70%
Crosswalk
60%
50%
88.6% 87.4%
40%
65.9%
30%
Stopped or
48.2%
20% Stopping
10%
0%
Flash Yellow Solid Yellow Solid Red Flash Red
Signal Phase
post conditions. The maximum queue length was defined as was observed between queues in the inside and outside lanes.
the longest pedestrian-induced queue length that was observed Vehicle queue statistics are shown separately for entry and
during or just after a pedestrian crossing. Queues were mea- exit lanes.
sured relative to the crosswalk and therefore do not include Exhibit 63 shows that the average maximum queue length
additional vehicles that were waiting to enter the roundabout increased from 2.3 to 5.0 vehicles at the entry and from 1.5 to
downstream of the crosswalk (at the entry). Vehicle queues 3.9 vehicles at the exit over both approach lanes. The increases
are combined for both lanes since no significant difference in average maximum queues are significant at p < 0.0001.
With available queue storage of two vehicles (one per lane) at
the exit leg, it is evident that the maximum queue sometimes
Exhibit 63. Maximum queue length statistics for
spilled back into the circulating lane, although the average
PHB installation.
queue is expected to be less than the reported max queue. The
Maximum Vehicle Queues for Both Lanes (in Vehicles) queue spillback effect is also evident in Exhibit 64, which shows
Pre Avg. Min. Max. Std. Dev. the cumulative distributions of maximum queue lengths. The
Entry (n = 104) 2.3 0.0 10.0 2.4 dashed line in Exhibit 64b represents the available queue stor-
Exit (n = 104) 1.5 0.0 9.0 1.8 age at the exit leg.
Total (n = 208) 1.9 0.0 10.0 2.1 Exhibit 64 shows a shift in the cumulative queue distribu-
Post tion toward higher queues associated with the installation of
Entry (n = 104) 5.0 0.0 19.0 3.9 the PHB. The largest effect is a significant reduction in the
Exit (n = 104) 3.9 0.0 18.0 3.0 occurrence of zero queues in the post condition, which results
Total (n = 208) 4.4 0.0 19.0 3.5 in the large discrepancy at queue length equal to zero. However,
