Which is the role of driver- or passengers-sex on the severity of road crashes?

Aim: The aim of the study is to quantify the main ways in which the sex of the driver/occupant of a passenger car affects the severity of road crashes. Methods: All 171 230 cars occupied by the driver and one or more passengers included in the Spanish Register of Victims of Road Crashes from 2014 to 2020 were included. We designed two cohort studies: In the first one, we estimated the Incidence Rate Ratios (IRR) between the sex of the drivers and the occurrence of any death and/or severe injuries among their passengers. In the second one we estimated the conditioned IRR between the sex of the occupants of the same car and their risk of death and/or severe injuries. We used fixed Poisson models to obtain IRR estimates, crude and adjusted by individual- environment- and vehicle-related variables. Results: A consistent inverse relationship between driver's female sex and passenger's severity was found, (IRR 0.72, 95 % CI 0.68-0.77), stronger for single crashes (IRR 0.67, 95 % CI 0.60-0.65). The magnitude decreased after adjusting for vehicle- and environment-related variables (IRR 0.82, 95 % CI 0.73-0.92). In the second study, the risk of death or hospitalization was higher for occupants of female sex (IRR 1.23, 95 % CI 1.17-1.30). Conclusions: The risk of death or severe injuries among passengers of cars involved in single crashes is lower for female drivers, probably due to safer driving. On the contrary, in similar crashes, the risk of injuries leading to hospitalization is higher for females.