Analysing crash severity on expressways in India: statistical and machine learning models

The high injury severity of traffic crashes on Indian expressways is a significant concern for road safety experts, although studies dedicated to this critical issue are limited. The present study investigates the factors influencing crash severity using multinomial logit (MNL), decision tree (DT) and random forest (RF) models on a dataset of 2747 crashes on three selected expressways. The dependent variable, crash severity, had four injury severity categories: fatal, severe, minor and property damage only (PDO). Various explanatory variables included traffic and speed characteristics, temporal and geometric characteristics, primary contributing factors, crash type and the vehicles involved. Synthetic minority oversampling (SMOTE) and randomised class balancing (RCB) techniques were also employed to tackle the class imbalance issue in the dataset. The predictive performance of models was evaluated using classification accuracy and kappa value. The RF model showed the highest predictive accuracy on the RCB dataset. The key findings highlight the critical need for enforcement of speed limits and entry restrictions, lane discipline and improvement of design deficiencies, such as provisions of truck lay-bys and bus bays. These measures can help in policy-making and engineering improvements to enhance road safety on expressways in India.