Crash base rates for freeways/reduction strategies for rear end crashes.

A safety analysis of a specific location includes a "base crash rate" analysis for identifying crash patterns at the study location. If the calculated crash rate for any crash type at a particular location is found to be higher than the "base crash rate", then that location is chosen for further study to determine if a safety problem actually exists at that location and, if so, what counter measure(s) can be used. The primary objective of this study was to develop a set of mathematical models to estimate base crash rates for freeways in Ohio. The models estimate the incremental changes in the dependent variables (crash rate for different types of crashes)resulting from changes in the independent variables including geometric features, operational controls, and environmental conditions. The base crash density/rate models were developed for the following crash types: (a)Injury crashes, (b) PDO crashes, (c) Total crashes, (d) Angle crashes, (e) Fixed crashes, (f) Rear end crashes, (g) Sideswipe crashes, (h) Wet road crashes, and (i) Night crashes. To evaluate the complex interaction among the dependent and independent variables, Automatic Interaction Detection (AID) technique was used. After the completion of AID analysis, stepwise multiple regression technique was used to develop mathematical models for the split groups. Finally, the models were validated with the one-third data that was set aside for validation. This study developed state-wide and district-wide base crash density and rate models for freeways. These models are recommended for use by ODOT for evaluating freeway crashes. The results of this study have a high potential of implementation in Ohio