Abstract
The empirical Bayesian method, currently the industry standard for before-and-after collision analysis, was used to perform post hoc tests on the efficacy of high-visibility school (yellow, continental-style) crosswalks in the city of San Francisco, California. Statistical analysis compared the number of collisions predicted for the after period had the enhanced crosswalks not been installed with the number of collisions observed. The analysis used data for 54 treated intersections with high-visibility crosswalks and 54 control intersections, each chosen for its geographical proximity to a treated intersection. The results from this analysis suggest a statistically significant reduction in the numbers of collisions at the intersections with high-visibility crosswalks. The estimated reduction is 37%, with the 95% confidence interval ranging from 13% to 60%. Potential limitations of this analysis, including a constant traffic volume input over time and a background reduction in collisions citywide, are discussed. In addition to the safety benefit attributable to high-visibility crosswalk markings, high-visibility crosswalks likely contribute to a sense of pedestrian comfort and overall design amenity. Future studies would enhance these results by evaluating other factors that may affect pedestrian safety at school crosswalks, such as changes in driver or pedestrian behavior and increased awareness of crosswalks and pedestrian activity.
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