6.2.3 Interactive Highway Safety Design Model (IHSDM)

IHSDM is a suite of software analysis tools developed to evaluate the safety and operational effects of geometric design decisions on roadways. IHSDM is meant to be used as a decision-support tool by providing estimates of the expected safety and operational performance of a roadway design. It checks existing or proposed roadway designs against relevant design policy values. The results of the IHSDM support decision-making in the roadway design process. This software is intended to be used by project managers, designers, and traffic safety reviewers in State and local agencies and by engineering consulting firms. As of 2024, the IHSDM software is available for free from the FHWA software overview site, but FHWA no longer supports development of this software. A link to the software is located in
Appendix G, Section 5 – External References (Reference 4)
, and includes the following six evaluation modules:
  • Crash Prediction;
  • Design Consistency;
  • Intersection Review;
  • Policy Review;
  • Traffic Analysis; and
  • Driver/Vehicle
The crash prediction module was developed to help support the implementation of the HSM Part C and is considered a faithful implementation of the HSM predictive method. The crash prediction models in Chapter 10, Chapter 11, Chapter 12, Chapter 18, and Chapter 19 are included in IHSDM, along with other crash prediction models developed since the publication of the HSM. IHSDM crash prediction modules can be used to do the following
  • Predict crash frequency for roadway segments, intersections, and interchanges;
  • Evaluate the safety effects of roadway improvements and treatments;
  • Compare relative safety performance of design alternatives; and
  • Assess the safety and cost-effectiveness of design decisions
The following facility types can be analyzed with IHSDM:
  • Rural Intersections and Two-Lane, TwoWay Segments;
  • Rural Multi-Lane Segments and Intersections;
  • Urban/Suburban Arterial Segments and Intersections;
  • Roundabouts; and
  • Freeways, Ramps, and Interchanges
Data entry and segmentation can be done manually, as in the HSM spreadsheets. The software also has the capability to import alignment files to automate parts of the data entry and segmentation process. Data can also be copied and pasted in from another spreadsheet to increase the usability. Data can be entered either based on milepost or station. Additional information about facility types and data considerations is available in the help feature of the IHSDM software.