Continued reliance on traffic signals: the cost of missed opportunities to improve traffic flow and safety at urban intersections

September 2005

Traffic congestion and motor vehicle crashes are widespread problems, especially in urban areas. Opportunities to improve traffic flow and safety can be missed when traffic signals are installed at locations suitable for roundabouts. The present study examined ten signalized intersections in Northern Virginia that were newly constructed or recently modified. Standard traffic engineering algorithms were used to estimate the effects on traffic delays and motor vehicle crashes if these intersections had been constructed as roundabouts. It was estimated that roundabouts would have reduced vehicle delays by 62-74 percent, depending on the intersection, 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. Based on previous research on crash risk, it is estimated that construction of roundabouts in place of traffic signals could have prevented 62 crashes, 41 with injuries, between 1999 and 2003 at five of the intersections for which crash data were available. These results show the magnitude of the traffic flow and safety costs when traffic signals are installed at locations suitable for roundabouts.