Application of the IHSDM: A Case Study

Initially released for two-lane rural highways, the Interactive Highway Safety Design Model (IHSDM) is one of the latest tools developed by the Federal Highway Administration (FHWA) for practicing professionals. The IHSDM is a road safety evaluation software that allows highway planners and designers to assess safety and operational performance of a roadway corridor. The IHSDM currently has five evaluation modules: Policy Review, Intersection Review, Crash Prediction, Design Consistency, and Traffic Analysis. The IHSDM was selected as one tool used in the evaluation of improvement alternatives for a two lane rural highway with an extensive history of injury and fatal crashes. Through implementation of the IHSDM for the 23-mile study corridor, a number of valuable lessons were learned. Use of the IHSDM is data intensive and can be complicated by a lack of available data, poor quality data, and inconsistent stationing among the various data elements. For this reason, the IHSDM is best suited for the design community, where recent survey data and consistent CADD-based design parameters allow for a smooth transition into the IHSDM framework. Others intending to use the IHSDM for preliminary design activities should clearly identify the goals of the analysis and the data needs prior to starting the project to ensure that adequate data are readily available. Model calibration to local conditions is an integral part of comparing design alternatives with the IHSDM software (the type of analysis may impact the level of calibration necessary). Evaluation results should be checked for reasonableness and FHWA should be consulted for issues identified with model operation. Although the 2004 version of IHSDM has been released, FHWA continues to refine the model based upon user testing and feedback.