The Interactive Highway Safety Design Model (IHSDM) is a suite of software analysis tools for evaluating safety and operational effects of geometric design decisions on highways. It is a decision-support tool for individual locations, and is not intended to be used as a safety management tool for an entire network. Intended users include highway project managers, designers, and traffic and safety reviewers in State and local highway agencies and engineering consulting firms. IHSDM currently includes six evaluation modules:

• Crash prediction module: Estimates the expected frequency of crashes on a highway using geometric design and traffic characteristics. IHSDM is a faithful implementation of the predictive methods in the Highway Safety Manual (HSM).
• Design consistency module: Estimates the magnitude of potential speed inconsistencies to help identify and diagnose safety issues at horizontal curves of existing highways or proposed designs.
• Intersection review module: Performs a diagnostic review to systematically evaluate an intersection design for typical safety concerns.
• Policy review module: Checks highway segment design elements for compliance with relevant highway geometric design policy at several stages during the highway design process.
• Traffic analysis module: Estimates operational quality-of-service measures for an existing or proposed design under current or projected future traffic flows.
• Driver/Vehicle module: Estimates a driver’s speed and path along a highway and corresponding measures of vehicle dynamics.

All modules can be applied on two-lane rural highways. Only the crash prediction module is applicable to other facility types, such as four-lane rural highways, urban and suburban arterials, and freeways.