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OCR for page 118
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attributable to the smaller inscribed diameter and associated at the PS-RAL roundabout, which may be related to the prox-
lower design speed of the roundabout. imity to a major college campus. The PS-RAL site further
suggests lower yielding at the roundabout exit leg, which is
not evident at DAV-CLT.
Crossing Statistics
Exhibit 26b shows the yield utilization rates at the two sites.
The analysis of crossing performance focuses on aspects A lower yield utilization rate is evident at DAV-CLT (67.4%)
of pedestrianvehicle interaction following the NCHRP than at PS-RAL (85.4%). Both sites suggest a slightly higher
Project 3-78A analysis framework. The first analysis compo- yield utilization rate at the exit leg. By combining yielding
nent describes the availability and utilization of yields in both and yield utilization rates, it can be stated that the PS-RAL
the pre and post treatment conditions. Two yield measures site exhibits a higher likelihood of crossing in a yield than
are used in the analysis: DAV-CLT. The range of observed yield utilization points to
differences in crossing abilities among participants, with some
· P(Y_ENC): The probability of encountering a yield event, utilizing 100% of yields while others don't utilize any.
defined as the number of yields divided by the total of all The analysis next considered the availability and utilization
events encountered by the pedestrian until he/she completes of crossable gaps. For the purpose of this analysis, a crossable
the crossing. gap is defined as a gap that was sufficient to cross the width of
· P(GO|Y): The probability of yield utilization, defined as the crosswalk at a walking speed of 3.5 ft/s, while allowing for
the number of crossings in a yield divided by total number a 2-s safety buffer. This 2 s allows for some pedestrian reaction
of yields encountered by the pedestrian. time before initiating the crossing, as well as a safety buffer
between a completed crossing and the next vehicle arrival. The
The P(Y_ENC) measure is somewhat different than the resulting crossable gap thresholds for DAV-CLT and PS-RAL
traditionally used probability of yielding, since it is calculated were 7 s and 6 s, respectively. Similar to the yield statistics,
on the basis of all pedestrianvehicle events and not just two gap-related parameters are defined:
potential yielders. Chapter 3 provides additional discussion
on these and other performance measures, including examples · P(CG_ENC): The probability of encountering a CG event
on the difference between the yielding measures. (gap greater than CG threshold), defined as the number of
Exhibit 26a compares the yield encounters for the two sites. crossable gaps divided by the total of all events encountered
It shows generally higher probabilities of encountering a yield by the pedestrian.
Exhibit 26. Yield encounters and utilization statistics
for studied crosswalk.
a) P(Y_ENC)
DAV-CLT Avg. Min. Max. Std. Dev.
Entry 5.8% 0.0% 14.3% 4.8%
Exit 6.7% 0.0% 20.0% 5.0%
Overall 6.3% 0.0% 20.0% 4.9%
PS-RAL
Entry 37.9% 13.1% 66.7% 17.8%
Exit 28.1% 8.1% 58.3% 14.4%
Overall 33.0% 8.1% 66.7% 16.6%
b) P(GO|Y)
DAV-CLT Avg. Min. Max. Std. Dev.
Entry 64.1% 0.0% 100.0% 41.2%
Exit 70.4% 0.0% 100.0% 44.1%
Overall 67.4% 0.0% 100.0% 42.3%
PS-RAL
Entry 83.0% 50.0% 100.0% 20.4%
Exit 87.8% 60.0% 100.0% 14.1%
Overall 85.4% 50.0% 100.0% 17.3%
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Exhibit 27. Crossable gap encounters and utilization Exhibit 28. Average pedestrian delay statistics for
statistics for studied crosswalk. studied crosswalk.
a) P(CG_ENC) a) Observed Delay per Leg (s)
DAV-CLT Avg. Min. Max. Std. Dev. DAV-CLT Avg. Min. Max. Std. Dev.
Entry 29.8% 18.5% 44.7% 6.9% Entry 26.6 11.2 74.0 17.0
Exit 27.8% 9.1% 40.0% 6.7% Exit 24.0 11.4 41.8 9.7
Overall 28.8% 9.1% 44.7% 6.8% Overall 25.3 11.2 74.0 13.8
PS-RAL PS-RAL
Entry 17.7% 0.0% 30.0% 8.9% Entry 10.5 4.1 34.2 8.9
Exit 20.5% 0.0% 32.0% 9.7% Exit 11.6 5.2 26.7 6.8
Overall 19.1% 0.0% 32.0% 9.2% Overall 11.1 4.1 34.2 7.8
b) P(GO|Gap>Min) b) Delay>Min (s)
DAV-CLT Avg. Min. Max. Std. Dev. DAV-CLT Avg. Min. Max. Std. Dev.
Entry 66.3% 25.0% 100.0% 20.6% Entry 18.8 4.8 59.4 15.5
Exit 60.3% 33.3% 100.0% 17.9% Exit 17.2 5.2 35.1 9.6
Overall 63.3% 25.0% 100.0% 19.3% Overall 18.0 4.8 59.4 12.8
PS-RAL PS-RAL (Min = 6 s)
Entry 52.0% 0.0% 100.0% 41.3% Entry 5.6 0.8 24.7 7.2
Exit 63.6% 18.8% 100.0% 26.6% Exit 6.1 0.8 19.4 5.8
Overall 57.8% 0.0% 100.0% 34.4% Overall 5.8 0.8 24.7 6.4
· P(GO|CG): The probability of crossable gap utilization, the trial started and when the pedestrian initiated the
defined as the number of crossings in a CG divided by total crossing.
number of CGs encountered by the pedestrian. · Delay>Min (s): The delay beyond the first opportunity
(Delay>Min), defined as the time difference between first
Exhibit 27 shows the statistics for the studied crosswalks. yield or crossable gap encountered by the pedestrian and
Exhibit 27a shows the encounters of crossable gaps at the the actual crossing initiation.
two sites. Following the definition above, the minimum cross-
able gaps for DAV-CLT and PS-RAL are approximately 7.0 and Statistics for all measures are for crossing one leg of the
6.0 s, respectively. The table shows that DAV-CLT has a slightly roundabout at either the exit or entry approach. The total
higher rate of gaps (28.8%) that are greater than the crossable average delay by crossing can be calculated by summing delay
gap than PS_RAL does (19.1%). For both sites, the gap occur- statistics for the entry and exit legs.
rence is comparable for entry and exit legs. Exhibit 28a compares the observed delay experienced by the
Exhibit 27b shows gap utilization rates for DAV-CLT of blind pedestrians at both sites and suggests significantly lower
approximately 60%. At PS-RAL the gap utilization rate is higher delays at PS-RAL. Interpreting this difference in light of the
for the exit leg than the entry leg, with 63.6% and 52% utiliza- results in Exhibits 3 and 4, the lower delay is likely attributable
tion, respectively. Overall, the gap utilization rates across the two to greater P(Y_ENC) and greater P(GO|Y) at this site. The delay
sites are comparable. Combining gap occurrence and utiliza- at DAV-CLT correspondingly is higher because pedestrians
tion, there is a somewhat higher likelihood of crossing in a gap wait for crossable gaps in the absence of yields. The delay is
at DAV-CLT. The range of gap utilization again varies between comparable for the entry and exit leg at both sites. The average
0% and 100%, emphasizing the need for a sufficient sample size total delay to get across both entry and exit lanes represents
given the variability of crossing behavior. In this context it is also the sum of the two estimates.
important to point out that no utilized gaps below the defined Exhibit 28b shows the delay beyond the first crossing
crossable gap threshold were observed at either site, giving opportunity for both sites. The findings are similar to those
confidence to the assumed crossable gap thresholds. in Exhibit 28a, with pedestrians at PS-RAL experiencing less
The combined effect of gap and yield availability and utiliza- unnecessary delay compared to DAV-CLT. Again, the reason
tion is reflected in the delay experienced by pedestrians. Delay for the differences is likely related to P(Yield) and P(GO|Y).
statistics in Exhibit 28 are provided for two delay measures: The difference in delay suggests that a crossing opportunity is
utilized more quickly at PS-RAL. If these sites were analyzed
· Observed Delay per Leg (s): The average pedestrian delay using LOS definitions in the HCM, the average delay times at
in seconds, defined as the time difference between when PS-RAL and DAV-CLT (approximately 11 and 25 s) would
