#02 - Cross Walk Discussion - Laserfiche WebLink

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17 In short, using either analysis approach—grouping comparison sites or using an analysis that matches marked and unmarked sites—produced nearly identical results. The discussion below includes results of both analysis approaches. Estimation of Daily Pedestrian Volume At each of the 2,000 crossing sites, at least 1 hour-long count of pedestrian street crossings was conducted. Based on the time of day of the count, an expansion factor was used to compute an approximate pedestrian ADT. At a given observation site, i, a count ni is made of pedestrians crossing the street during some interval of time Ti. Now, from a standard pedestrian volume by time of day distribution, the proportion pi of daily pedestrian traffic expected during Ti can be determined. If ni ≠ 0, an estimate of the daily total pedestrian volume is made by, Ni = ni/pi. This estimate has the property that if Ni was known, then the estimated pedestrian volume during the interval Ti would be Nipi = ni, the observed number. A detailed discussion of how pedestrian ADTs were determined based on short-term pedestrian crossing counts is given in appendix A. Calculation of Pedestrian Crash Rates Assuming that motor vehicle volumes, speeds, and other site features remain constant, it is reasonable to expect that the number of pedestrian crashes will increase as the number of pedestrians crossing the street (pedestrian exposure) increases. When comparing sites to see which has the greatest risk of a pedestrian crash, it is necessary to control for the number of pedestrians. The pedestrian crash rate is a more appropriate measure of safety than the total number of pedestrian crashes for comparing the relative safety of marked and unmarked crosswalks, particularly since pedestrian crossing volumes differ at marked and unmarked crosswalks. In this study, crash rates were calculated in terms of crashes per million pedestrian crossings. For example, if an average of 1,000 pedestrians cross an intersection every day, then there will be 365,000 (or 0.365 million) pedestrian crossings in a year. The number of pedestrian crashes in a year is then divided by 0.365 million times the number of years to get the pedestrian crash rate. Determination of Crash-Related Variables The following analysis was conducted to determine which traffic and roadway variables have a significant effect on pedestrian crashes. Table 1 shows some summary values of pedestrian volumes and crashes for marked and unmarked crosswalks categorized by number of lanes. For each marked crosswalk, a closely matched unmarked comparison site was chosen—usually a nearby site on the same street. Quite often, the comparison site was the opposite approach to the same intersection (on the same road). As a result of this matching, the distributions of site characteristics, including traffic volumes, should be essentially the same for marked and unmarked sites. Pedestrian volumes were recorded at a marked crosswalk and its matched unmarked location at essentially the same time of day and for an equal period of time. Thus, pedestrian volumes were free to vary between marked and unmarked sites but were collected in such a way as to represent equal proportions of expected daily pedestrian traffic at the respective locations.