THE RELATIONSHIP OF CRASH RISK TO GEOMETRY AND CROSS-SECTION ON AUSTRALIAN RURAL ROADS

This paper reports a study which brings together information on road geometry (curvature and grade), cross-section, traffic flow and crashes. The study used a geographic information system (GIS) to relate the different information streams. Road geometry data was available from pre-existing surveys carried out using an instrumented vehicle (Gipsi-Trac), and this data was used to build an electronic map using the ARCINFO GIS. Width of traffic lanes, shoulders and shoulder seal was determined by site inspection and added to the GIS. Traffic flow data was also added. Crashes were located on the GIS using information in the sketch maps and narratives in the police accident reports. The ARCINFO software allows links to be established between the crash database and the ARCINFO map. The analysis indicates that crash rate varies more in response to horizontal curvature than grade, that crash rate increases only for very sharp curvature, but the increase in rates can be large at these values, that lane width has little impact on crash rates, and that sites with shoulder seal have lower crash rates than sites without shoulder seal, although there is conflicting evidence as to whether wider seals improve safety compared to narrow seals. Analysis by logistic regression generally confirmed these results. (a) For the covering entry of this conference, please see IRRD abstract no. 492019.