Extending the Highway Safety Manual (HSM) framework for traffic safety performance evaluation

Traffic safety performance evaluation, especially in agencies charged with safety investments, has primarily followed the methods outlined in the Highway Safety Manual (HSM). The HSM is a seminal start in ushering the field toward a systematic way of evaluating traffic safety. This paper presents a case for a more comprehensive framework to enable broader evaluation of safety performance based on a literature review of advanced methods.The presented framework integrates network-screening methods with pure outcome-based methods, multivariate fixed-parameter extensions of the HSM safety performance functions, and multivariate random parameter extensions. The paper suggests agencies should assess and choose methods for safety performance evaluation based on three criteria: (1) integrability with network-screening techniques, (2) data requirements, and (3) model predictive performance.This paper intends to help practitioners and researchers identify critical issues that underlie the establishment of comprehensive safety performance evaluation frameworks. To this end the paper discusses the pros and cons of the various methods, databases for the methods, and the importance of the methods for treatment of emerging databases such as roadside inventories. The presented framework is intended to provide guidance to state agencies in selecting safety evaluation methods given organizational constraints.