A note on hotspot identification for urban expressways

• Justify that the traditional frequency based approaches are not appropriate for urban expressways.
• Propose a societal risk based hotspots identification approach.
• Compare the consistency of various candidate approaches.
• Conclude that societal risk based EB method is the best choice for urban expressways.

Hotspot identification (HSID) is of great importance to land transport authorities (e.g. the Land Transport Authority (LTA) of Singapore) in their efforts to improve the safety of highways. According to a survey of experienced engineers at the LTA of Singapore, we draw the conclusion that the severity of crashes should not be neglected in the HSID process. Accordingly, in this technical note, societal risk-based simple ranking and empirical Bayesian methods are proposed to identify the hotspots in a Singapore expressway on the basis of the detailed three-year casualty data in the Historical Crash Damage (HCD) database. We further conduct a consistency analysis to compare the societal risk-based method and the conventional frequency-based method. The consistency analysis reports that (1) the frequency-based method is more consistent than the societal risk-based method, and (2) the empirical Bayesian method is more consistent than the simple ranking method.