High friction surface treatment (HFST) is a pavement and safety treatment that dramatically and immediately increases pavement friction to reduce crashes, injuries, and fatalities associated with friction demand issues. Understanding the effectiveness of HFST as a safety measure is crucial for estimating the expected crash reduction and evaluating the cost-effectiveness of future HFST implementations. Existing research on HFST safety effectiveness evaluation is limited to horizontal curves and ramps, despite the promising safety benefits of installing HFST at other locations, such as signalized intersections. To help fill this research gap, this paper presents a rigorous before-and-after safety effectiveness evaluation of HFST installation at signalized intersections using traffic and crash data obtained from 15 treatment sites and 90 control sites in British Columbia, Canada. To enhance the validity of the safety assessment, two before-and-after evaluation methods were applied: empirical Bayes and full Bayes. The results indicated statistically significant safety benefits of HFST at the treated sites. Specifically, the estimated reductions in serious (fatal and injury) crashes, serious rear-end crashes, and serious wet-pavement crashes, are about 51%, 57%, and 64%, respectively. It is worth noting that an unexpected decline in crashes was observed at the control sites, which introduces some uncertainty in interpreting the results and warrants careful consideration.
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