Weather as a chronic hazard for road transportation in Canadian cities

Inclement weather creates a chronic hazard for Canadian travellers. Past studies indicate that road collision rates increase during precipitation, although the magnitude of the increase varies from study to study, partly as a result of variations in weather and driving conditions, but also because of differences in methods. The goal of the current study is to improve our understanding of the links between weather and travel risk in mid-sized Canadian cities by using a standardized method for analyzing data from six cities with different climates: Halifax-Dartmouth, Ottawa, Quebec, Hamilton, Waterloo Region, and Regina. The study has four interrelated objectives: (1) To conduct a sensitivity analysis to determine the extent to which risk estimates vary depending on the criteria used to define precipitation events and 'normal' conditions; (2) To compare the relative risk of collision and injury during precipitation relative to 'normal' conditions; (3) To determine the extent to which weather-related risks vary for different Canadian cities; and (4) To explore any differences in collision characteristics between events and controls, especially as they vary from city to city. Results are based on a matched-pair analysis, using six-hour time blocks over a four-year period, 1995 to 1998. Results indicate only modest sensitivity to the criteria used to define precipitation events and 'normal' conditions. On average, precipitation is associated with a 75 percent increase in traffic collisions and a 45 percent increase in related injuries, as compared to 'normal' seasonal conditions, but risk levels vary depending on the characteristics of the weather event. Both sensitivity to specific weather conditions and weather-related accident profiles vary from city to city in ways that are not easily explained.