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81
reduced that delay by 56% and 42% to 6.3 s and 39.4 s, trians within a given time interval. Clearly, this assumes per-
respectively. The use of a two-stage phasing at the same prox- fect pedestrian compliance with the signal phasing.
imal location resulted in delay reductions of 71% and 64%
over the base case even if a regular pedestrian signal was used. Discussion
The PHB resulted in further delay benefits and reductions of
89% and 92% over the base case. This chapter has discussed two extensions of the NCHRP
Modified crossing geometries such as a zigzag or distal Project 3-78A field results for application to other locations,
crosswalk resulted in similar delay savings for both a regular geometries, and traffic volumes. The first part of this chap-
pedestrian signal and the PHB phasing scheme. In all cases ter presented empirically derived mixed-priority pedestrian
the PHB resulted in additional delay savings. The modified delay models that can be used to estimate pedestrian delay at
exit leg geometry for the zigzag and distal crosswalk locations single-lane roundabouts, two-lane roundabouts, and CTLs.
can further reduce spillback potential into the circulating lane The explanatory variables in these delay models are consis-
tent with the four behavioral probability parameters defined
due to added vehicle storage at the roundabout exit lane. The
in Chapter 4 and used in the Chapter 5 evaluation of field
detailed analysis results in Appendix L discuss the average and
results. The second part presented the concept of using these
maximum vehicle queues at the crosswalk in light of the avail-
four probability terms in a microsimulation environment for
able queue storage.
further extension analysis. Microsimulation tools have the
The analysis further suggested a non-monotonic relation-
advantage that the analyst can readily explore the impacts
ship between the treatment effects and the levels of vehicle
of different geometries, traffic volumes, and pedestrian and
volumes. Pedestrian-induced vehicle delays appeared to be
driver behavior on selected performance measures.
greatest as traffic volumes approached roundabout capacity.
The constraint of both approaches is their limited applica-
The need for innovation in pedestrian signal application is
bility to measures of pedestrian safety. The chapter briefly
therefore less pronounced at low traffic volumes but should touched on the ability to extract surrogate safety measures
be a key consideration at busy roundabout junctions. As from simulation in the form of pedestrianvehicle conflicts
vehicle volumes increase, pedestrian signals become even or near collisions. This approach is the focus of an ongoing
more important from an accessibility perspective. The most national effort by FHWA but has yet to be extensively vali-
promising approach for minimizing the impacts on vehicu- dated. This research has demonstrated that it is possible to
lar traffic while ensuring access for blind pedestrians appears extract pedestrianvehicle conflict data from simulation and
to be a strategic reduction of the vehicle red indication. The further that the rate of conflicts is responsive to changes in the
authors showed that this can be achieved by shortening the four underlying probability parameters. Presumably, changes
crossing distance through a two-stage crossing or through in these parameters represent the implicit impacts of pedes-
the introduction of a "Flashing Red" phase in a PHB phasing trian crossing treatments. However, while there is confidence
scheme. in the delay measures resulting from such analysis, the risk
A sensitivity analysis of the effect of increasing pedestrian measures are at this point strictly theoretical.
volumes supported the hypothesis that vehicle and pedestrian The concept of predicting pedestrianvehicle conflicts from
delay impacts increase at a diminishing rate as signal opera- simulation requires extensive field validation to build confi-
tions approach the limit of maximum number of actuations dence in the approach. While this research recorded a field
per hour. Pedestrian and vehicular delays generally appear to measure of risk in the form of O&M interventions, its occur-
plateau at volumes in excess of 200 pedestrians/hour. This rence and variability across participants makes it challenging
suggests an application for signalization as a means of con- to perform such validation. Further, while some of the tested
trolling pedestrian interference to vehicular operations--an treatments showed a significant impact on these O&M inter-
interesting twist to the existing pedestrian signal warrant that ventions, additional observations are needed to validate a
evaluates only the available crossing opportunities for pedes- simulation-based safety performance assessment.
