The Highway Safety Design Manual (HSM) shares the Interactive Highway Safety Design Model’s (IHSDM’s) goal of providing quantitative safety analysis tools to decisionmakers.

The HSM is a Transportation Research Board (TRB) and American Association of State Highway and Transportation Officials (AASHTO) initiative (published by AASHTO) to provide the best factual information and tools in a useful and widely accepted form and to facilitate roadway design and operational decisions based upon explicit consideration of their safety consequences. The HSM is organized into four parts:

1. Introduction and Fundamentals
2. Roadway Safety Management Process
3. Predictive Methods (see table below comparing HSM and IHSDM)
4. Crash Modification Factors

The following table compares the types of predictive methods and types of facilities targeted by the HSM and IHSDM. The first edition of the HSM, published in June 2010, provides predictive methods for rural two-lane highways, rural multilane highways, and urban and suburban arterials with five lanes or fewer. With the 2009 Crash Prediction Module Beta Release (June 30, 2009), Federal Highway Administration (FHWA) expanded the scope of IHSDM to include the HSM crash prediction methods for multilane rural highways and urban and suburban arterials with five lanes or fewer. The Crash Prediction Module of the IHSDM – HSM Predictive Method 2021Release includes a faithful software implementation of Part C of the First Edition HSM, containing predictive methods for rural two-lane highways, rural multilane highways, and urban and suburban arterials. In addition, the 2021 Release includes predictive methods for freeway segments and freeway ramps/interchanges including ramps, collector-distributor (C-D) roads, and ramp terminals, based on the HSM 2014 Supplement. Crash prediction methods for 6+ lanes and 1-way urban/suburban arterials were added to IHSDM in 2016, based on materials developed under NCHRP Project 17-58, for inclusion in the future Second Edition HSM. Crash prediction methods for roundabouts were added in 2019, based on materials developed under NCHRP Project 17-70, and documented in NCHRP Research Report 888 (Development of Roundabout Crash Prediction Models and Methods). Crash prediction methods for some intersection types not covered in the HSM 1st Edition were added in 2021, based on materials developed under NCHRP Project 17-68, and documented in NCHRP Web-Only Document 297 (Intersection Crash Prediction Methods for the Highway Safety Manual). A calibration utility assists agencies in implementing the calibration procedures described in the Appendix to Part C of the HSM. The IHSDM Economic Analysis Tool allows IHSDM users to do economic analyses using Crash Prediction Module (CPM) evaluation results crash frequencies and severities within IHSDM.