Citation

Liu G, Popoff A. Transp. Res. Rec. 1997; 1595: 8-13.

Copyright

(Copyright © 1997, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

10.3141/1595-02

PMID

unavailable

Abstract

The latest speed limit increases in the United States have brought about debates about the relationship between travel speed and traffic safety. The relationship between travel speed and collision severity is clear: Increase in travel speed leads to a dramatic increase in collision severity. However, the relationship between speed and collision involvement is more complicated. Examined here is the relationship between travel speed and collision involvement on Saskatchewan provincial highways. Saskatchewan data indicate that the most prevalent source of human error contributing to collisions may be speed-related. The study of the relationship between vehicle speed and collisions therefore is fundamental for developing countermeasures to achieve compliance with speed regulations and to reduce the number of collisions. According to nine provincial-wide speed surveys and corresponding accident data from the last 26 years, traffic casualties and casualty rates on provincial highways are closely correlated to the surveyed average travel speed. This finding is not surprising, considering the fact that about 60 to 80 percent of all collisions on provincial highways are single-vehicle collisions. The relationship indicates that casualties will be reduced by about 7 percent for every 1-km/hr (0.62-mph) reduction in average travel speed on provincial highways. Casualty rates on provincial highways are closely correlated to speed differentials--higher speed differentials lead to higher casualty rates. Some difficult issues relating to speed and safety are also discussed.