How to Develop and Use SPFs

Summary of State SPF Calibration and Development Efforts
Safety performance functions (SPFs) are one of the fundamental building blocks of the predictive methods in the HSM. One step in implementing the HSM is calibration of the HSM-provided SPFs or development of jurisdiction-specific SPFs. Many States have already completed this step. This spreadsheet (updated in November 2020) summarizes the results from States that have published and posted their SPF calibration factors and/or State-developed SPFs.

Summary of State-Adapted HSM Part C Spreadsheet Tools
Part C of the HSM provides predictive methods for estimating predicted and expected crash frequency and severity for several roadway types. Among the HSM training tools developed under NCHRP Project 17-38 was a set of Microsoft Excel spreadsheets for performing the HSM Part C calculations for two-lane two-way rural roads, multilane rural roads, urban and suburban arterials. NCHRP Project 17-45 developed ISATe, an Excel-based spreadsheet tool for freeways and ramps. Several States have adapted these spreadsheets for production purposes and to reflect their regional crash data. This table provides a summary of State-adapted HSM Part C spreadsheet tools.

Safety Performance Function Decision Guide: SPF Calibration vs SPF Development
This guidebook is intended to provide guidance on whether an agency should calibrate the safety performance functions from the Highway Safety Manual or develop jurisdiction-specific SPFs. The guidebook discusses the factors that need to be considered while making the decision. It is intended to be of use to practitioners at state and local agencies and to researchers.

Safety Performance Function Development Guide: Developing Jurisidiction-Specific SPFs
This guidebook is intended to provide guidance on developing safety performance functions from the Highway Safety Manual. The guidebook discusses the process to develop jurisdiction specific SPFs. It is intended to be of use to practitioners at state and local agencies and to researchers.

User's Guide to Develop Highway Safety Manual Safety Performance Function Calibration Factors
The use of Highway Safety Manual crash predictive models in any jurisdiction calls for calibration of safety performance functions and replacement of crash severity and collision type distribution tables and adjustment factors to local and current conditions. This Guide's aim is to support the development of calibration factors and the adaptation of crash distribution tables and adjustment factors to local and current conditions.

*Additional Resource: Appendix B Excel Tables for use with HR 20-7(332) Guide for SPF Calibration Factors