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OCR for page 138
138
Exhibit 64. Cumulative distribution.
a) Entry Leg
1
0.9
Cumulative Frequency
0.8
0.7
0.6
0.5
0.4
0.3
PRE
0.2
0.1 POST
0
0 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 15 16 17 18 19 20
Queue Length in Both Lanes (in Vehicles)
b) Exit Leg
1
0.9
Cumulative Frequency
0.8
0.7
0.6
0.5
0.4
0.3
0.2 PRE
0.1 POST
0
0 1 2 3 4 5 6 7 8 9 1 0 11 12 13 14 15 16 17 18 19 20
Queue Length in Both Lanes (in Vehicles)
it is evident that very few long queues were observed in either ated a more uniform distribution of delay across participants.
the pre or post condition. With two lanes of storage, any total The PHB further reduced the overall number of pedestrian
queue greater than two vehicles at the exit leg will cause some vehicle interaction events, with far fewer rejected crossing
spillback into the circle, as shown by the dashed line. With the opportunities. The reason for this was that drivers yielded
installation of the PHB, that proportion of maximum queues (stopped at the light), thereby reducing the number of gaps
greater than two vehicles increased from 29.8% to 69.2%. encountered.
However, the average queue is expected to be much lower, so Most drivers complied with the signal indication, although
that the overall effect of the PHB installation on vehicle queues there was evidence for both misunderstanding (waiting until
is considered to be marginal. In fact, a determined yielder is "Blank" to proceed) and non-compliance (proceeding through
likely to cause similar if not more delay to a driver waiting at a red signal) on the part of drivers. It is expected that these num-
the efficient PHB signalization scheme, as evident by some bers may improve with additional public information material
long queues observed in the pre study. or enforcement. The installation of the PHB caused a marginal
increase in vehicle queuing, although it is difficult to extra-
PHB Crosswalk Summary polate that effect to higher-volume roundabouts. The analysis
did confirm that queues caused by determined yielders can
In summary, the installation of the PHB or HAWK signal approach queues caused by the signal. Further, since many driv-
resulted in a large reduction in delay and elimination of O&M ers did not proceed through the "Flashing Red," the post queues
interventions for all study participants. The relative difference are longer than expected with the PHB scheme. The impact on
between pre and post studies was greatest for participants that queues is therefore expected to be reduced with improved pub-
experienced high delays in the pre condition since the PHB cre- lic education and driver understanding of the PHB.
OCR for page 139
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Overall, the installation of the PHB greatly increased the Exhibit 65. Summary performance statistics
availability and utilization of crossing opportunities, which is pre and post PHB installation.
reflected in a reduction in pedestrian delay. The PHB further
Performance Measure Pre Post
reduced O&M interventions to zero, suggesting enhanced
Yield Availability* 29.7% 72.5%
safety performance. Exhibit 65 summarizes these key metrics
Gap Availability* 28.7% 45.0%
for the PHB evaluation.
Yield Utilization* 68.9% 95.0%
But even given the improved pedestrian performance and
Gap Utilization* 88.2% 100.0%
the marginal vehicle impact, care needs to be taken extra- 85th Percentile Delay (s) 29.8 8.7
polating these results to higher-volume scenarios or round- O&M Interventions 2.4% 0.0%
abouts with different geometry. The PHB does appear to be a
*Average of near and far lane
viable treatment for two-lane roundabouts, but it needs to be
combined with pedestrian and driver education, as well as
enforcement, to maximize its impact.
