The Impact of Lowered Residential Speed Limits in the City of Edmonton

In 2010, the City of Edmonton reduced the posted speed limit (PSL) in six residential communities from 50 to 40 km/h. This study investigates the impact of the reduced limit on vehicle speeds using a before-after experimental design with control group adjustment. Continuous speed and traffic flow data were collected at 65 locations for a period of 7 months, including 1 month as a baseline for the before period and 6 months representing the after period. Speed evaluation was performed at several levels ranging from individual speed survey locations to an overall aggregate analysis. Several performance indicators such as mean free-flow speed, speed variance, level of compliance, mean speed of speeders (drivers exceeding the PSL), and percentile speed profile were considered. The results revealed a statistically significant reduction in mean free-flow speed and speed variances for all combinations of time of day and day of week classifications. Though the compliance to the PSL was low after the limit reduction, compliance to a 15 km/h threshold above the PSL was significantly high. Moreover, the analysis showed that the effectiveness of the reduced PSL improved with time.