Abstract Foggy conditions are considered to be potentially dangerous for drivers and have been paid considerable attention recently. However, few studies have addressed the influence of fog-related conditions on injury severity in accidents, particularly at highway-rail grade crossings. This study estimates the effect of foggy conditions on driver injury severity at highway-rail grade crossings. Compared to accidents occurring during clear conditions, fog-related accidents tend to result in more severe injuries. Older drivers are more likely to suffer severe injuries in foggy than in clear conditions as a result of their poorer vision and reaction times. In foggy conditions, drivers were found to be willing to drive at speeds that were too high for them to be able to stop to avoid obstacles that they may be able to identify and react to. In addition, drivers in foggy conditions are more likely to be severely injured in accidents occurring in open space areas with passive control device due to low traffic volumes and higher expected vehicle speeds. Drivers are more likely to experience high level injury in accidents during early morning in winter. Finally, drivers tend to suffer more severe injuries in accidents during peak-hours as a result of the fatigue that they experience at these times.