An evaluation of a Vision Zero traffic-calming intervention, an urban transportation safety policy

Today over 40 major metropolitan areas in the United States have formally adopted a new “Vision Zero” road design framework to prioritize roadway safety and eliminate traffic-related fatalities. This policy framework diffused across much of Europe and, more recently, the United States. In 2019, the City of San Francisco, California, implemented a series of traffic-calming interventions designed to lower speeds on left-hand turns and thereby reduce severe pedestrian and bicyclist injuries. This study uses a quasi-experimental design to evaluate this innovation. Results show that these safety measures reduced speeds between 1.4 and 1.9 miles per hour and that these reductions were sustained for at least 1 year. A conservative cost-benefit analysis suggests that these interventions have a large, positive return on investment, and that they are justified for any intersection with 2.5 or more pedestrian- or cyclist-involved crashes over a 5-year window.