Abstract An observational survey was conducted on 11.961 vehicles in Southern Ontario to determine car driver seat belt use. Major variables included geographical location, road type. sex of driver and size of vehicle. Overall usage rate was 48.6% and was higher in the large city and higher for expressways than non-expressways. Seat belt use was inversely related to car size across all survey sites and geographical locations. Sex differences in usage rates were found to interact with variables of geographical location and road type.