Saftey performance of freeway sections and relation to length of speed-change lanes

The design of freeway entrances and exits requires managing the high operating speeds on the through lanes and the intense lane-change manoeuvres due to merging and diverging. Therefore, adequate lengths between these entrances and exits and provision of adequate speed-change lanes would help drivers execute such tasks safely. Most of the previous research has focused on analyzing operational conditions of the merge and diverge areas based on kinematic analysis of speeds and distances. However, little research has addressed the safety effects of merging and diverging and the interrelationship with geometric features. In this study, 26 interchanges were selected to quantify the effects of ramp terminal spacing and traffic volumes on safety performance through regression analysis. Negative binomial models were developed using 5 year collision data. Modelling attempts resulted in several statistically significant models relating traffic volumes and geometric features to collision frequency.