Effect of Residential Street Speed Limit Reduction on Driving Speeds in Portland, Oregon

Abstract

This study analyzed the impacts on motor vehicle observed speeds following a residential speed limit reduction from 40.23 km/hr (25 mi/hr) to 32.19 km/hr (20 mi/hr) in Portland, OR that was accompanied by a public awareness and signage campaign. The study used before and after observations of vehicle speeds collected by pneumatic tube traffic counters. Overall, the analysis suggests that the reduction of posted speed limits to 32.19 km/h (20 mi/h) has resulted in lower observed vehicle speeds and fewer vehicles traveling at higher speeds. The reduction in the percentage of vehicles traveling above 48.28 km/h (30 mi/h) (-1.7%) and 56.33 km/h (35 mi/h) (-0.5%) are larger in magnitude than other speed metrics.