This paper will assess the short-term effects on driver speeds after increasing the posted speed limit on rural four-lane highways in Saskatchewan. On June 1, 2003 the maximum speed limit on select sections of Saskatchewan twinned highways was increased from 100 km/hr to 110 km/hr. Spot speed studies were conducted at representative locations before and after the speed limit increase, during the period from April 2003 to September 2003. While the majority of the data collected was on the four-lane highway system, data was also collected on two-lane highway sections to identify any possible “halo effects” where speed limits were not increased. Data collected at the study sites before the increase indicated that the 100 km/hr speed limit was well below the average driver speed and 85th percentile speed. Data collected after the speed limit increase showed only a minimal increase in average driver speeds, 85th percentile speeds, and pace speeds, while the average increase in speed differential was found to be minimal. The speed limit increase appears to have created a higher driver compliance rate, at least in the short term. The increased compliance rate does not necessarily reflect a change in driver behavior, but may be the result of a change in how compliance is measured. Speed profiles on two-lane highways only showed small changes in vehicle speed characteristics. Overall, raising the posted speed limit has had a lesser effect on driver speeds than anticipated. Due to the short duration of the study, additional studies are recommended to further identify vehicle speed trends and possible changes in collision profiles.
