Guidance for posted speed limit reductions in support of vision zero

Reducing posted speed limits can lower average and 85th percentile vehicle speeds, particularly in areas where speeding was already prevalent, though the overall impact is often modest and varies by roadway context. Analysis across Calgary, Edmonton, and Montreal shows that changes in driver behavior do not always scale with the reduction in posted limits, and shifts in compliance metrics can reflect the new threshold rather than significant behavioral change.

Effectiveness is strongly influenced by roadway design. Streets with narrower lanes, sidewalks, and more constrained environments are more likely to see meaningful speed reductions, while wider, straighter roads with medians often require additional measures such as traffic calming, enforcement, or education. Connected vehicle data also enables proactive monitoring of speed behavior and supports the development of predictive safety models to guide more targeted Vision Zero strategies.