Development of Volume-to-Capacity Based Accident Prediction Models

This study focused on developing relationships between accident rates and the capacity of the roads, particularly the rural interstate highways. Accident prediction models were developed that used the V/C (volume/capacity) as a predictor variable. A concept of modified capacity is introduced, where the design capacity is adjusted to incorporate other geometric factors. This modified capacity includes variables that represent surface rates, surface types, inside shoulder width, and others that may have significant impacts on the accident occurrence, which are not directly weighed when capacity is calculated. A model presented here is for rural interstate highways. Data are based on an averaged data set of six years. This model is part of a more comprehensive study where several models were created, not only for rural interstate highways but also for urban interstate highways, rural and urban two-lane highways, and urban and rural multilane highways.