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Interactive Highway Safety Design Model (IHSDM): Related Initiatives


Two related initiatives share IHSDM’s goal of providing quantitative safety analysis tools to decisionmakers:

  • Highway Safety Manual (HSM).
  • SafetyAnalyst.


The Highway Safety Manual 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 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. The Crash Prediction Module of the IHSDM – HSM Predictive Method 2013 Release is a faithful software implementation of Part C of the 1st Edition HSM, containing predictive methods for rural two-lane highways, rural multilane highways, and urban and suburban arterials. In addition, the 2013 Release includes a Beta version of predictive methods for freeway segments and freeway ramps/interchanges (including ramps. collector-distributor (C-D) roads, and ramp terminals), based on draft HSM materials. A Calibration Utility assists agencies in implementing the calibration procedures described in the Appendix to Part C of the HSM.


Facility Type Policy Review Crash Prediction Diagnostic Review
Two-Lane Rural Highway IHSDM (2003) IHSDM (2003)
HSM (2010)
IHSDM (2003)
Multilane Rural Highway   IHSDM (2009)
HSM (2010)
Urban and Suburban Arterial   IHSDM (2009)
HSM (2010)
Freeway Segments   IHSDM (2012; Beta)
HSM (2013; Draft)
Freeway Ramps/Interchanges   IHSDM (2013; Beta)
HSM (2013; Draft)


The SafetyAnalyst was developed by FHWA and is now an AASHTOWare product. It provides state-of-the art analytical tools for use in the decision-making 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.

  Safety Analyst IHSDM
Scope Network-Level Project-Level
Target Project Selection Decisions Geometric Design Decisions