Application of IHSDM highway safety modelling to New Zealand

The Interactive Highway Safety Design Model (IHSDM) is a suite of evaluation tools for assessing the safety impacts of geometric design decisions. Developed over almost a decade by the US Federal Highways Administration (FHWA), this publicly available software can help planners and designers identify and assess treatments for potential safety problems on existing or proposed highway sections. The initial development effort focused on two-lane rural highways, making IHSDM also very applicable to the bulk of New Zealand's state highway network. However a number of tasks have been required to make IHSDM appropriate for New Zealand conditions. These include calibrating the crash prediction model to reflect local patterns, incorporating a set of New Zealand-specific design policies and standards, validating the speed prediction model, modifying the model’s vehicle fleet, and developing a means of importing existing road geometry data into IHSDM. This paper reports on the work required to undertake these tasks and test the revised model’s applicability to New Zealand highways. Case studies of actual rural realignments are being used to check IHSDM’s practical usability and its crash rate predictions.