The impact of lowered residential speed limits on vehicle speed behavior

• This study investigated the effect of residential speed limit reduction on speed.
• A before-and-after experimental design with control group was employed.
• Speed and traffic volume data was collected for a period of 7 months.
• Mean free-flow speed, speed variance, compliance, etc., were compared.
• Speed limit reduction was found effective in terms of all performance measures.

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 PSL on vehicle speeds using a before-and-after experimental design with a control group adjustment. Continuous speed and traffic flow data was collected at 65 locations over a period of 7 months, with the first month representing the before period and the following 6 months representing the after period. Speed evaluation was performed on 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, 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 absolute compliance to the reduced PSL was low, 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.