Calibration of Overseas Highway Crash Prediction Models for New Zealand - a Case Study with IHSDM

Crash prediction models (CPMs) are an increasing feature of rural highway design practice internationally. A significant related development was the Interactive Highway Safety Design Model (IHSDM) in the US. However it would be difficult for every country to develop similar design tools with the same degree of complexity and research. Research has recently been exploring ways to assess the safety performance of rural highways in New Zealand. IHSDM was identified as worthy of further investigation, and a number of tasks were undertaken to adapt it for use in NZ. These included developing suitable data importing routines and calibrating IHSDM's CPM to match NZ crash patterns. A series of validation tests assessed IHSDM's effectiveness in predicting the relative safety of NZ rural roads. These included a “before and after” crash comparison of a major highway realignment, and checks of crash numbers along highway lengths in varying terrain. The investigations showed that IHSDM is a promising tool for safety and operational assessment of highway alignments (both existing and proposed) in NZ. However, IHSDM’s current lack of consideration for bridges and inconsistent road elements limit the ability of its CPM to assess sub-standard existing routes with as much accuracy as well-designed newer alignments