Environment

Improved Air Quality

Many vehicles must wait for the light to turn green in a signalized intersection. While stopped, the vehicle's exhaust emits more undesirable pollutants and gases into the atmosphere. Because roundabouts often eliminate such stops and improve traffic flow, they also reduce vehicle emissions and fuel consumption. In one study, replacing traffic signals and signs with roundabouts reduced carbon monoxide emissions by 32%, nitrous oxide emissions by 34%, carbon dioxide emissions by 37% and hydrocarbon emissions by 42%. Another study by Kansas State University study found that replacing four-way stops with roundabouts reduced carbon monoxide emissions by 38-45% and carbon dioxide emissions by 55-61%. Nitrogen oxides dropped 44-51%, and hydrocarbons fell 62-68%.

Reduced Fuel Costs, Noise Pollution and Time Savings

In fall 2005, the Insurance Institute for Highway Safety studied 10 intersections where traffic signals were built instead of roundabouts. The study estimated vehicle delays and fuel consumption at the signalized intersections and then compared the results to what they would have been if roundabouts had been built instead. For those 10 intersections, roundabouts would have:

  • Reduced delays by 62-74%, saving 325,000 hours (37 years) of motorists' time annually.
  • Decreased fuel consumption by about 235,000 gallons per year, for an annual savings of $705,000 (assuming an average cost of $3.00 per gallon of regular gas).