Pedestrian Signal Safety - AAA Foundation for Traffic Safety

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TRAFFIC OPERATIONS ANALYSIS
Table E-12 shows the intersection operational and geometric characteristics for the Montgomery
County case study intersection. Figure E-4 shows the overall average vehicle delay (AVD) and
intersection level of service (LOS) under various peak-hour traffic volume and pedestrian walking
speed scenarios (3.00, 3.50, 4.00 ft./sec. and base conditions).
Figures E-5, E-6, and E-7 show the major street and minor street approach AVD (in sec.) under
walking speeds of 3.00 ft./sec., 3.50 ft./sec., and 4.00 ft./sec., respectively. Table E-13 shows the
overall, major street approach, and minor street approach intersection LOS and AVD (in sec.) under
various peak-hour traffic volume scenarios and under pedestrian walking speeds of 3.00 ft./sec., 3.50
ft./sec., and 4.00 ft./sec.
The modeled peak-hour volumes at the Montgomery County case study intersection ranged from a
decrease of 10 percent to an increase of 10 percent of existing peak-hour volumes. The existing LOS
at this case study intersection for the 3.00 ft./sec. pedestrian walking speed scenario was at capacity
(LOS E with a corresponding average delay of 60 sec. per vehicle).
When comparing existing volume conditions to a modeled increase of 5 percent above existing
volume conditions, the LOS designation (LOS E) did not change; however, there was a corresponding
increase in average delay per vehicle (ADPV) of approximately 9 sec. under the 3.00 ft./sec. walking
speed scenario. An incremental increase of another 5 percent of peak-hour volume (to 10 percent
above existing volumes) at the 3.00 ft./sec. walking speed lowered the LOS from E to F and added
49 sec. to the ADPV. Thus, from existing volume conditions to a modeled increase of 10 percent
over existing volumes, there was a reduction of two LOS designations (from LOS D to LOS F) and a
corresponding increase in 58 sec. to ADPV.
Under the 3.50 ft./sec. and 4.00 ft./sec. walking speed scenarios, under existing volumes to an
increase of 10 percent of existing volumes, there was no change in LOS (LOS D); however, there
was a corresponding increase in ADPV of 6 sec. and 4 sec. under the 3.50 ft./sec. and 4.00 ft./sec.
walking speeds, respectively.
Thus, under the conditions analyzed, the 3.00 ft./sec. pedestrian walking speed, as compared to the
3.50 ft./sec. and 4.00 ft./sec. pedestrian walking speeds, had a greater negative impact on vehicular
traffic operations at the case study intersection.
For the major street approach, under existing conditions, LOS ranged from LOS D for the 3.50 ft./
sec. and 4.00 ft./sec. walking speed assumptions to LOS E for the 3.00 ft./sec. assumption. The
mean vehicle delay under existing volume conditions for the 3.50 and 4.00 ft./sec. walking speed
assumptions was 45 sec.
For the 3.00 ft./sec. walking speed assumption, AVD was 66 sec. This represents an increase of 21
sec. in AVD under the 3.00 ft./sec. walking speed assumption. In comparison to some of the other
case study intersections analyzed, this delay would be noticeable to a driver.
The range in ADPV under existing volume conditions as compared to a modeled increase of 10
percent above existing volumes for the 3.00 ft./sec. walking speed scenario was 66 sec. to 140 sec.
(this represents an increase in AVD of 74 sec.). LOS was reduced from LOS E under existing volume
conditions to LOS F when the volumes were increased to 10 percent above existing volumes.