The safety effects of the ageing driving population have been a topic of research interests in health and transportation economics in recent years due to the ageing of the baby boomers. This study adds to the current knowledge by examining the marginal effects of changing the driver mix on injury crashes using data from the Canadian Province of Alberta between 1990 and 2004. Results from a Poisson regression model reveal that increasing the number of young and ageing drivers will result in an increase in the number of injury crashes whereas increasing the number of middle-aged drivers will result in a reduction. These results are in contrast to those obtained in a previous study on the marginal effects of changing the driver mix on fatal crashes in the Australian State of Queensland and some possible explanations for the differing results are provided.