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24 Table 8. Crashes, exposure proportions, expected crashes, and binomial probabilities for categories of marked crosswalks. Number of Lanes Median Type Traffic Volume (ADT) Am pm E(Am) P (a > Am) Two – < 8,000 15 .6173 15.43 .6541 Two – > 8,000 19 .6382 20.42 .7631 Multi Not raised < 3,000 0 .6443 0 – Multi Not raised 3,000–6,000 3 .6612 2.64 .8529 Multi Not raised 6,000–9,000 0 .7985 1.60 1.00 Multi Not raised 9,000–12,000 12 .7741 12.39 .7149 Multi Not raised 12,000–15,000 23 .7383 18.46 .0242 Multi Not raised > 15,000 91 .7535 73.08 .000002 Multi Raised < 9,000 2 .8035 1.61 .6456 Multi Raised 9,000–15,000 3 .7500 2.25 .4219 Multi Raised > 15,000 20 .5919 13.61 .0041 pm= Proportion of pedestrian exposure at marked crosswalks. Am = Actual number of pedestrian crashes at the marked crosswalks. E(Am) = Estimated (predicted) number of pedestrian crashes at marked crosswalks. P(a > Am) = Binomial probabilities. Comparisons of Pedestrian Age Distribution Effects Each pedestrian in both the crash and exposure samples was classified into one of seven age categories: 12 and under, 13–18, 19–25, 26–35, 36–50, 51–64, and 65 and over. Across the entire set of sites, the two age distributions differed substantially, with a considerably higher proportion of young adults (19– 35) in the exposure sample (compared to other age groups), and a much higher proportion of the oldest age group in the crash sample. The difference was statistically significant, χ26df = 216.86, p = .001. The data were then partitioned into four subsets determined by marked or unmarked crosswalks on streets having two lanes or having three or more lanes. The same general pattern of the exposure and crash age distributions tended to hold on the subsets. In particular, the crash distribution tended to always be higher for the oldest pedestrian group. The relatively small sample sizes of crashes in some of the subsets necessitated combining some of the age categories to obtain a valid statistical comparison of the distributions. Marked crosswalks on two-lane roads. There were 33 crashes in this subset. With seven age categories, several cells had expected counts of fewer than five, so the two youngest and the two oldest age groups were combined. It might be noted, however, that 7 of the 33 crashes (21.2 percent) involved pedestrians in the 65-and-over age group, compared to 3.4 percent in the exposure sample. The five- category collapsed distributions differed significantly (χ24df = 11.00, p = .027). Of the crash-involved pedestrians, 30.3 percent were in the 51-and-over age category, compared to 13.2 percent in the exposure sample. Unmarked crosswalks on two-lane roads. Only 21 pedestrian crashes occurred in this subset. Again, five-category age distributions were used for the statistical test. While the percentage of crash-involved pedestrians in the oldest age category (51 and older) was higher than that of the exposure sample (19.1 percent versus 10.8 percent), the distributions overall did not differ significantly (χ24 = 4.40, p = 0.354).