A Statistical Evaluation of the Collision-Reduction Efficacy of High-Visibility School (Yellow) Crosswalks in San Francisco

摘要

Two nonparametric statistical methods: Pearson's Chi-Squared Test and the Wilcoxon Signed Rank Test, were used to perform tests on the efficacy of high-visibility school (yellow, continental-style) crosswalks in the City of San Francisco. Statistical analysis with the two methods compared collision data before and after the installation of the crosswalks, as well as across matched pairs of treated (those with yellow, high-visibility crosswalks) versus control (those with conventional (parallel, white) crosswalk striping) sites. The analysis controlled for background trends in collisions (those not associated with the high-visibility markings), as well as the general locations of the intersections. Results from this analysis suggest there has been a general downward trend in pedestrian collisions throughout the city, but there has not been an additional, statistically significant reduction in collisions at the intersections with high-visibility, yellow crosswalks compared to those with conventional crosswalk striping. Although the study did not document a safety benefit attributable to high-visibility crosswalk markings, to the extent that the high-visibility crosswalks contribute to a sense of pedestrian comfort and overall design amenity, they may still be justified. Future studies would enhance these results by evaluating other factors that may contribute to improved pedestrian safety at school crosswalks, such as changes in driver and/or pedestrian behavior and increased awareness of crosswalks and pedestrian activity. In addition, future studies using the Empirical Bayesian statistical evaluation method could strength this analysis.