The importance of exposure in explaining accident patterns has been recognized for at least 50 years. A method is outlined for using existing origin-destination data, in conjunction with a geographic information system, to estimate risk exposure for specific driver groups in urban areas. The method is developed for drivers age 60+ years in the region of Waterloo, Ontario, Canada. Results were validated by three criteria. First, comparisons of simulated trips with stated-preference routes showed a high degree of correspondence at the route/system level. Second, simulated travel patterns were fairly consistent with what would be expected given the spatial and temporal distribution of not-at-fault drivers. Third, the geographic information system results were combined with accident data to calculate involvement rates. These were then compared with estimates for the province of Ontario. Again, risk patterns were found to be similar at the aggregate level. In conclusion, geographic information system technology provides a novel and promising method for estimating risk exposure from origin-destination data.