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<br /> <br />Table 1. Pedestrian crashes and volumes for marked and unmarked crosswalks. <br />No. of Lanes Type Sites Ped. <br />Vol.* <br />Avg. Ped. <br />ADT/site <br />Number of <br />Ped. Crashes <br />Avg. <br />Yrs.** <br />2 Marked <br />Unmarked <br />456 <br />458 <br />176,345 <br />104,922 <br />387 <br />229 <br />37 <br />23 <br />4.81 <br />4.81 <br />3 or 4 Marked <br />Unmarked <br />401 <br />395 <br />104,237 <br />37,941 <br />260 <br />96 <br />94 <br />12 <br />4.59 <br />4.60 <br />5 or more Marked <br />Unmarked <br />143 <br />147 <br />31,266 <br />11,955 <br />219 <br />81 <br />57 <br />6 <br />4.65 <br />4.60 <br />All Marked <br />Unmarked <br />1,000 <br />1,000 <br />311,848 <br />154,818 <br />312 <br />155 <br />188 <br />41 <br />4.70 <br />4.70 <br />*Ped. Vol. = Sum of the pedestrian ADT at sites within a given grouping (by number of lanes). <br />**Avg. Yrs. = Average number of years of crash data per site. <br /> <br />The pedestrian ADT per site was 312 at marked crosswalks and 155 at unmarked crosswalks, as shown in <br />table 1. Thus, 66.8 percent of this pedestrian volume occurred at marked crosswalk sites. A total of 229 <br />pedestrian crashes were recorded at these 2,000 sites over a period of roughly 5 years. If marked and <br />unmarked crosswalks were equally safe (or unsafe), then given that 229 crashes occurred, it would be <br />expected that 66.8 percent of them (153 crashes) would have occurred at marked crosswalk sites. This <br />expected number is considerably smaller than the actual number of 188 observed at marked crosswalks. <br />Under the hypothesis of equal safety, and conditional on 229 total crashes, the probability of observing <br />188 or more crashes at the marked sites can be obtained from the binomial distribution with parameters, <br />p = .668 and n = .229, as <br /> <br /> (1) <br /> <br />Thus, the hypothesis of equal safety across the entire set of sites would be rejected. <br /> <br />On the other hand, there may be subsets defined by various site characteristics where such a hypothesis <br />would not be rejected. For example, consider the first two rows of table 1, which refer to sites on streets <br />having two lanes. At these sites, 62.7 percent of the pedestrian volume occurred on marked crosswalks. <br />Of the 60 crashes that occurred at these sites, 37.6 crashes would be expected at the marked crosswalk <br />sites compared with the observed count of 37. Clearly, the hypothesis of equal safety could not be <br />rejected for this subset of sites. In other words, for the two-lane road sites in the database, there was no <br />significant difference in pedestrian crashes between marked and unmarked crosswalks. <br /> <br />From the rows of table 1 corresponding to three- or four-lane roads and roads with five or more lanes, the <br />observed crash frequencies for the marked crosswalk sites are 94 and 57, respectively. Both totals <br />considerably exceed the expected values of 77.6 and 45.7 based on proportions of pedestrian exposure at <br />these sites. The probabilities of observing values this extreme by chance are: <br /> <br /> (2) <br /> <br />and <br /> <br /> (3) <br /> 18