#02 - Cross Walk Discussion - Laserfiche WebLink

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27 The final model provides a framework to test the hypothesis of whether marked crosswalks have the same expected number of pedestrian crashes in 5 years controlling for the effects of pedestrian ADT, vehicle traffic ADT, number of lanes, and presence of a raised median. Because the interaction between traffic ADT and the indicator for marked crosswalk, ADT*CM ($9), was statistically significant, it was concluded that the presence of a marked crosswalk increases the expected number of pedestrian crashes in 5 years; however, the effect size is dependent on the traffic ADT and number of lanes. There is also a statistically significant interaction between pedestrian volume and the indicator for marked crosswalk, which was interpreted as the effect size of the presence of a marked crosswalk as dependent on the pedestrian volume. The lane indicator variables compare two lanes with five or more, and three or four lanes with five lanes or more. A two-degrees-of-freedom test for any lane effect has an associated p- value of 0.1071. The two median variables compare no median with other median, and raised median with other median. A two-degrees-of-freedom test for any median effect has an associated p-value of 0.0531. The number of lanes, type of median, pedestrian volume, and ADT are all intracorrelated. This correlation is evidenced by the fact that ADT increases as the number of lanes increases. Also, sites with two lanes do not have a median. The number of lanes was also included in the model and probably is expressed indirectly through ADT and median type. In the final model form, the regional effect was only marginally significant, and including the regional variables (i.e., western versus eastern region) into the model had virtually no influence on the crash effects of the other variables. Thus, the regional variable was not included in the final model. Further discussion of the final model relative to the goodness-of-fit measures, residuals, and possible biases of multicollinearity is contained in appendix B. In short, the final model was found to be valid and appropriate for the available database. A considerable amount of data exploration was also conducted during the analysis phase of study before developing the final model. Pedestrian Crash Plots The final pedestrian crash prediction model can be illustrated by inputting various values of pedestrian ADT, traffic ADT, number of lanes (two lanes, four lanes, or more), and median type (raised median or no raised median). All values used in the following figures (and in appendix B) are well within the actual distributions of the data sample. Figures 13 through 17 and the figures in appendix C (figures 45 through 64) all contain plots of response curves based on the final negative binomial prediction model. Each of these graphs shows a solid line for both marked and unmarked locations. For each solid line, there is a dashed line above and below it representing the upper and lower bounds of the 95 percent confidence intervals. The relationship of pedestrian crashes in a 5-year period is shown in figure 13 for a range of pedestrian ADTs for traffic ADT of 5,000 using the final crash prediction model. Notice that there is no difference in predicted pedestrian crashes in marked versus unmarked crosswalks for these conditions. Plots of pedestrian crashes in a 5-year period from the model are shown for two-lane roads as a function of traffic ADT in figure 14 (where pedestrian ADT = 300). Note that there is little if any difference in pedestrian crashes between marked and unmarked crosswalks, even for traffic ADTs as high as 15,000. In fact, for marked crosswalks with traffic ADT of 15,000 and 300 pedestrians per day, expected pedestrian crashes are 0.10 per 5 years, or 1 pedestrian crash per 50 years per site. Figure 15 illustrates the predicted pedestrian crashes for a five-lane pedestrian crossing with no median and a pedestrian ADT of 250. As traffic ADT increases, pedestrian crashes stay relatively consistent on