Prepared by:

Jean Andrey, University of Waterloo

Jeff Suggett, Synectics Transportation Consulting Inc.

Brian Mills, Meteorological Service of Canada

Mike Leahy, University of Waterloo

Inclement weather creates a chronic hazard for Canadian travelers. Past studies indicate that 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, Québec, Hamilton, Waterloo Region, and Regina.

The study has three 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; and (3) To determine the extent to which weather-related risks vary for different Canadian cities. Results are based on a matched-pair analysis, using six-hour time blocks over a four-year period, 1995 to 1998. Weather data are from the Meteorological Service of Canada; collision data are from Transport Canada’s TRAID3 database.

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. Snowfall effects are more pronounced than rainfall effects for collisions. The relative risk of injury is lower than the relative risk of collision for both rain and snow, but the values are still well above one, indicating that precipitation is a serious safety issue. Sensitivity to weather hazards varies from city to city in ways that are not easily explained.

For a complete copy of this paper, please contact: jsuggett@synectics-inc.net