scope:

The Highway Safety Manual Supplement includes Chapter 18, Chapter 19, and Appendix B to Part C.

Utilizing the predictive method established in the Highway Safety Manual, 1st Edition (2010), this Supplement provides a structured methodology to estimate the expected average crash frequency (in total, by crash type, or by crash severity) for both freeways (Chapter 18) and ramps (Chapter 19) with known characteristics, and involving vehicles of all types. Appendix B for Part C describes two specialized procedures to be used with the predictive methods presented in both chapters: The first is used to calibrate the predictive models to local conditions; the second, the Empirical Bayes Method, combines observed crash frequencies with the estimates provided by the predictive models.