The Highway Safety Software (HSS) implements Crash Prediction Models from Highway Safety Manual (HSM) 1st edition and the HSM Supplement, which means the following chapters are included:
- Chapter 10 – Rural Two-Lane, Two-Way Roads
- Chapter 11 – Rural Multilane Highways
- Chapter 12 – Urban and Suburban Arterials
- Chapter 18 – Freeways
- Chapter 19 – Ramps
HSS is designed to determine the predicted and expected number of crashes for segments and intersections following the Predictive Method, which is explained in the aforementioned HSM chapters. The basis of the Predictive Method is calculating a Safety Performance Function (SPF) and applying Crash Modification Factors (CMFs) based on certain geometric and safety feature data in the intersection/segment. Whenever Historical Crash data is available, HSS allows Empirical Bayes method implementation.
The Highway Safety Software also includes new methods developed as a product of research projects. These methods were implemented as published in the reports listed below, and may be adjusted when formally incorporated in a future release of the Highway Safety Manual:
- NCHRP Project 17-70 – Roundabouts
- NCHRP Project 17-68 (Chapter 3) – Intersections with All-Way Stop-Control
- NCHRP Project 17-68 (Chapter 4) – Three-Leg Intersections with Signal Control on Rural Highways
- NCHRP Project 17-58 (Chapter 5) – Urban and Suburban Segments with Six or More Lanes
- NCHRP Project 17-58 (Chapter 6) – Intersections of Urban and Suburban Arterials with Six or More Lanes
- NCHRP Project 17-58 (Chapter 7) – Urban and Suburban One-Way Arterial Roadway Segments
- NCHRP Project 17-58 (Chapter 8) – Intersections of Urban and Suburban One-Way Arterials
- NCHRP Project 17-68 (Chapter 5) – Intersections on High-Speed Urban and Suburban Arterials
- NCHRP Project 17-68 (Chapter 8) – Crossroad Ramp Terminals at Single-Point Diamond Interchanges
- NCHRP Project 17-68 (Chapter 9) – Crossroad Ramp Terminals at Tight Diamond Interchanges
- NCHRP Project 17-84 (Chapter 4) – Pedestrian and Bicycle Safety Performance Functions