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Related Initiatives

Two related initiatives share Interactive Highway Safety Design Model’s (IHSDM’s) goal of providing quantitative safety analysis tools to decisionmakers:

  1. Highway Safety Manual (HSM)
  2. Safety Analyst

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 arterials¾with 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 arterials¾with five lanes or fewer. The Crash Prediction Module of the IHSDM – HSM Predictive Method 2020 Release is 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 2020 Release includes predictive methods for freeway segments and freeway ramps/interchanges¾including 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). 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 results¾crash frequencies and severities¾within IHSDM.

Predictive Methods and Types of Facilities Targeted by the HSM and IHSDM
Facility TypeIHSDM Evaluation ModulesIHSDM
Analyses Tool
Policy ReviewCrash PredictionDiagnostic*
Two-Lane Rural HighwayIHSDM (2003)IHSDM (2003)
HSM (2010)
IHSDM (2003)


Multilane Rural HighwayIHSDM (2015) IHSDM (2009)
HSM (2010)
Urban and Suburban Arterial
(5 lanes or fewer)
 IHSDM (2009)
HSM (2010)
Urban and Suburban Arterial
(6+ lanes and 1-way)
Freeway Segments IHSDM (2012)
HSM (2014)
 IHSDM (2017)
Freeway Ramps/Interchanges IHSDM (2013)
HSM (2014)
 IHSDM (2017)
Roundabouts IHSDM (2019) IHSDM (2019)
*Design Consistency, Traffic Analysis, Intersection Review, and Driver/Vehicle Modules

The SafetyAnalyst was developed by FHWA and is now an AASHTOWare product. It provides state-of-the art analytical tools for use in the decisionmaking process to identify and manage a systemwide program of site-specific improvements to enhance highway safety by cost-effective means. The SafetyAnalyst includes tools for:

  • Network screening
  • Diagnosis and countermeasure selection
  • Economic appraisal and priority ranking
  • Evaluation of implemented improvements

The following table compares the scope and type of decisions targeted by the SafetyAnalyst and IHSDM.

Scope and Type of Decisions Comparison by Safety Analyst and IHSDM
 Safety AnalystIHSDM
TargetProject Selection DecisionsGeometric Design Decisions
Updated: Tuesday, October 27, 2020