IHSDM: Crash Prediction Module

The IHSDM 2009 Crash Prediction Module (CPM) Beta Release (June 30, 2009) – which is an implementation of the crash prediction methods documented in Part C of the Highway Safety Manual, Draft 3.1, April 2009 - includes capabilities to evaluate two-lane rural highways, multilane rural highways, and urban/suburban arterials. The IHSDM 2008 Public Release includes crash prediction capabilities for two-lane rural highways only.

The crash prediction module estimates the frequency of crashes expected on a roadway based on its geometric design and traffic characteristics. The crash prediction algorithms consider the effect of a number of roadway segment and intersection variables.

The algorithm for estimating crash frequency combine statistical base models and accident modification factors. Base models are available for roadway segments and for several types of intersections (e.g., three-legged intersections with stop control on the minor-road approach, four-legged intersections with stop control on the minor-road approaches, and four-legged signalized intersections for two-lane rural highways).

The accident modification factors adjust the base model estimates for individual geometric design element dimensions and for traffic control features. The factors are the consensus on the best available estimates of quantitative safety effects of each design and traffic control feature. The algorithm can be calibrated by State or local agencies to reflect roadway, topographic, environmental, and crash-reporting conditions (as documented in the Appendix to Part C of the Highway Safety Manual, Draft 3.1, April 2009). The algorithm also provides an Empirical Bayes procedure for weighted averaging of the algorithm estimate with project-specific crash history data.

The crash prediction module can provide input for scoping improvement projects on existing roadways, comparing the relative safety performance of design alternatives, and assessing the safety cost-effectiveness of design decisions.

See IHSDM Library for References.