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82
CHAPTER 7
Interpretation and Application
This chapter presents an interpretation of the findings of This framework allows the analyst to isolate different com-
research performed under NCHRP Project 3-78A in the con- ponents of the crossing task at crosswalks. Any treatments
text of application to engineering practice. The chapter ini- intended to improve the accessibility are specifically targeted to
tially presents a synthesis of the study approach, followed by one or more of the criteria. On the basis of these four analysis
a summary of the field studies performed during this project. dimensions, the report describes the development and imple-
It then discusses specific implications for facility design and mentation of a set of performance measures. The performance
accessibility considerations at the three tested facility types: measures include the probability of encountering crossable
channelized turn lanes, single-lane roundabouts, and two- gaps, P(CG_ENC), and yields, P(Y_ENC), and the probability
lane roundabouts. The chapter concludes with a discussion of utilizing these crossing opportunities, P(GO|CG) and
of future research needs and recommendations for follow-up P(GO|Y). These performance measures were used in field
work to this project. studies to quantify the first two accessibility criteria. The per-
formance measures are further hypothesized to affect criteria 3
and 4, the delay and safety experienced by the pedestrian
Synthesis of Approach
during the crossing. Chapter 4 of this report provides detailed
The results of NCHRP Project 3-78A have three principal descriptions and definitions of all performance measures.
components: (1) the formulation of a framework for describ- The present research effort serves to introduce a structured
ing accessibility, (2) field study results of blind pedestrian cross- and measurable framework for quantifying the principal
ing studies including treatment installation, and (3) approaches operational parameters of accessibility.
for extension of the findings to other locations. Second, the research conducted a total of 11 field studies at
First, the project devised an analysis framework for assess- multiple test locations involving crossing trials of blind study
ing the accessibility and usability of different crossings to participants. These included four studies at an intersection
pedestrians who are blind. While the framework was developed with CTLs, two of which were posttests after installing sound
in this project in light of specific challenges to this group of strips, lane delineators, and a pedestrian-actuated flashing
pedestrians, it has broader application to other pedestrian pop- beacon (one location only). Four studies were performed at
ulations. The accessibility framework quantifies the crossing two-lane roundabout crosswalks. Again, two were posttests
performance at a tested location in four dimensions: after installing a raised crosswalk and a pedestrian hybrid
beacon at the two studied crosswalks. The remaining three
1. Crossing opportunity criterion studies were performed at two single-lane roundabouts. One
Are there sufficient crossing opportunities in the form of the single-lane roundabouts was evaluated in a pretest and
of yields or crossable gaps? posttest design, but without treatment installation, to test for
2. Opportunity utilization criterion a learning effect in study participants with repeated exposure.
Are the crossing opportunities utilized by the pedestrian? A twelfth dataset, originally collected for a prior research
3. Delay criterion effort, was also included in the analysis. This dataset was also
Is a crossing opportunity taken within a reasonable time? for a single-lane roundabout. In total the field studies evalu-
4. Safety criterion ated approximately 3,300 individual crossing attempts by
Does the crossing interaction occur without a significant 56 different blind study participants in 12 studies at five
degree of risk? different sites.
