Derivation of a New Surrogate Measure of Crash Severity

Abstract

This paper proposes a new surrogate measure—aggregated severe crash metric (ASCM)—that is based on conflict studies and traffic simulations to allow relative comparisons and safety evaluations between intersection designs in relation to crash severity. A procedure was developed to determine the injury probability of a simulated traffic conflict by randomly assigning drivers and vehicles into that conflict and repeating the process multiple times. An experimental validation effort was conducted by simulating 12 intersections through the simulation package of VISSIM. The surrogate safety assessment model was used to extract useful conflict data as the entry into the model for estimating ASCM. Spearman rank tests indicated that ASCM was able to identify the relative safety among traffic facilities in relation to crash severity. Notably, ASCM outperformed Highway Safety Manual procedures in rank tests. Preliminary efforts to correlate ASCM to crashes and to use it as a crash predictor indicated that regression models were well fitted for ASCM and predicted the frequency of real severe (i.e., injury and fatality) crashes; this result suggests the model's potential to be linked directly to actual severe crash frequency.