Calibration of the Highway Safety Manual Predictive Models for Rural Two-Lane Roads for Vermont

Dr. James L. Sullivan, Research Projects Director , University of Vermont Transportation Research Center – November 2019

The final report is available here.


The UVM Transportation Center completed the development of Vermont specific calibration factors and updated safety-performance functions for the five undivided, two-lane, two-way rural road predictive models in the Highway Safety Manual Chapter 10 (namely, Roadway segments, Signalized four-leg intersections, Unsignalized intersections, Three-leg with minor-road stop-control, and Four-leg with minor-road stop-control). Having these calibration factors specific to Vermont will now permit VTrans and consultants to be able to predict crashes more accurately and therefore to better evaluate project alternatives based on safety. While the HSM has been out for several years, the VTrans had not been able to fully benefit from the use of the predictive models for two-lane rural roads for alternatives evaluation since they were not calibrated, and the results were judged to be uncertain.


The author would like to acknowledge VTrans for providing funding for this work. The VTrans project sponsor, Mario Dupigny-Giroux, provided invaluable support and supervision, and the input of the project TAC members was greatly appreciated:

• Mario Dupigny-Giroux (Traffic Safety Engineer, Office of Highway Safety)

• Johnathan Croft (GIS Database Administrator, Mapping)

• Sai Sarepalli (CCRPC Transportation Planning Engineer)

• Ben Tietze (Traffic Safety Design)

• Zoe Neaderland (Coordinator, Policy and Planning Section)

• Emily Parkany (Manager, Research Section)