Combining Safety Analysis Tools for Evaluation of Freeway Work Zones: A Case Study

Predictive methods are available in the Highway Safety Manual (HSM) to estimate the safety performance of various types of roadway facilities, including freeways. These methods were developed to provide predictions of crash frequency in periods of normal roadway operation. Additionally, research has been conducted on various aspects of work zone safety. However, there is a need to combine insights gained from these separate efforts so work zones can be more effectively designed and monitored, and safety performance of work zones can be improved in a cost-effective manner. To conduct a case-study analysis of safety performance of an active freeway work zone, the freeway safety prediction methodology from Chapter 18 of the HSM has been combined with work zone crash modification factors that were documented in NCHRP Report 627. This combination improved the predicted crash frequencies that were obtained from a direct application of the HSM methodology, which does not in itself account for work-zone-specific issues. This combined analysis, along with traditional crash data analysis methods like crash trees, crash rate analysis, and hot spot analysis, allowed work zone safety to be monitored more effectively.