The effect of weather on the severity of multi-vehicle crashes: a case study of Iran

Traffic crashes are a social problem around the world and climate change is one of the major environmental factors that cause road crashes. The severity of multi-vehicle crashes under different weather conditions was investigated in this study. Crash data for three levels of crash severity (i.e. crashes involving property damage only (PDO), injury or fatality) from six highways in Iran were evaluated. Ordered logit models were selected for the analysis because of the ordinal nature of crash severity. The final model consists of seven independent variables: temperature below -7 degrees C, temperature above 19 degrees C, rainfall exceeding 5 mm/d, working day of the week, density (vehicles/km), roadside equipment and season of the year. These variables were found to have significant values at 0.95 confidence intervals. The model also showed that the probability of occurrence of a PDO crash is 77.5%, while the probability of occurrence of injury and fatal crashes are 18.9% and 3.6%, respectively.