Posted by: Francis Koster Published: September 11, 2009

Roundabouts Beat Stop Lights, Reduce Air Pollution 20-30%…

Roundabouts Beat Stop Lights, Reduce Air Pollution 20-30%...

by Francis P. Koster, Ed.D.

Using “Roundabouts” instead of traffic lights or stop signs has been documented to save as much as 20 and 30% of fuel consumed at these intersections, with corresponding declines in solid and particulate pollutants. [1] One study in Vermont indicated that the magnitude of impact from roundabouts on Vermont statewide motor fuel use by a hypothetical installation of roundabouts in place of signals at 100 busy intersections would decrease total annual motor fuel use by approximately 1-2% of 1997 annual statewide gasoline consumption attributable directly to the roundabout, and another similar 1-2% by changes in land use density enabled by the roundabouts.[2] Put another way,  installing a rather modest number of roundabouts throughout the United States in a distribution similar to the Vermont study would save twice as much gasoline directly as drilling for offshore oil would produce under the model proposed during the 2008 election[3][4],  and would lessen air pollution instead of adding to it. (Note also that the life expectancy of the oil supply derived from off-shore drilling is finite, that saved by roundabouts is not).roundabouts2

The City of Carmel, Indiana. found that when roundabouts replaced tradtional intersections, accidents with injury reduced by 78%, and that cost of construction of a roundabout was $125,000 less than constructing an intersection with traffic lights per Mayor Jim Brainard

Two decades of intersection control modeling and software development and research establish that substantial fuel savings at busy intersections can be gained by employing roundabouts rather than traffic signals.  Reduced fuel consumption–and by extension pollution emissions and GHGs–are demonstrated through analysis of empirical data and modeling reported from existing US roundabouts and those under development.   This knowledge base is so well accepted that it is included as a modeling assumption in highway planning computer models[5], and is an acceptable (although grossly underused)  design tool.


[1] Varhelyi A (2002) The effects of small roundabouts on emissions.  Transportation Research Part D 7. pp. 65-71 (Elsevier Science, Oxford, UK).

[2] Canadian Transportation Research Forum, Vancouver, May, 2001.  Modern Roundabouts, Global Warming, and Emissions Reductions:  Status of Research, and Opportunities for North America



[5] Highway Capacity Manual compatible software, aaSIDRA

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