Guidance on Customization of Highway Safety Manual for Virginia

For increased accuracy of the results of the procedures in the Highway Safety Manual (HSM), states have been encouraged to customize the procedures with local data. One way to customize the procedures is to develop calibration factors and to apply them to the default safety performance functions in the HSM. However, other ways can accomplish customization. The Virginia Department of Transportation (DOT) wants to customize the HSM procedures for the state as accurately as its resources will allow. This study examined ways to customize procedures and then developed guidance that could help a highway agency choose the best customization option for its jurisdiction. The guidance was used to recommend the best option for Virginia by using empirical data. The analysis was limited to divided segments and four-leg signalized intersections of rural multilane highways because the Virginia DOT's database provides most of the data required for developing safety performance functions and calibration factors for these two site types. The developed guidance flowchart can be used by an agency interested in customizing the HSM procedures. The flowchart can be applied with a combination of expert opinion and data analysis; a greater reliance on data analysis would require more time and resources. The guidance flowchart was applied in Virginia: a combination of Virginia's statewide safety performance functions, district-group calibration factors, and district-specific crash proportions appeared to be the best option for the state.