Continued Reliance on Traffic Signals: The Cost of Missed Opportunities to Improve Traffic Flow and Safety at Urban Intersections

Motor vehicle travel can provide important mobility benefits, but can generate unintended public health consequences, such as injury crashes and air pollution. Intersections are a major source of crashes and vehicle emissions, especially in urban areas. Research shows that the modern roundabout -- an alternative to traditional intersection designs -- can significantly reduce crashes and injuries while simultaneously enhancing mobility for pedestrians and motorists, and thereby reduce vehicle emissions. In this study, these research results are used to develop an estimate of the size of the benefits that were foregone in the Washington, DC metropolitan area when traffic signals were installed at ten intersections suitable for roundabouts. Standard algorithms were used to estimate effects on traffic delays and motor vehicle crashes if these intersections had been constructed as roundabouts. Roundabouts would have reduced vehicle delays by 62-74%, thus eliminating more than 300,000 hours of vehicle delay on an annual basis. Annual fuel consumption would have been reduced by more than 200,000 gallons, with commensurate reductions in vehicle emissions. An estimated 62 crashes could have prevented between 1999 and 2003 at five of the intersections for which crash data were available. If only 10 percent of US signalized intersections were converted to roundabouts, the estimated annual savings in lives and fuel could be approximately 250 fewer deaths and 5 million fewer gallons of fuel consumed, with commensurate reductions in vehicle emissions.