Modern Roundabouts Help Achieve Sustainability Goals? Circle Gets the Square!

Authors: Timothy Garceau*, Central Connecticut State University
Topics: Transportation Geography, Urban and Regional Planning, Urban Geography
Keywords: Transportation, Sustainability, Traffic Calming, Air Quality
Session Type: Paper
Day: 4/12/2018
Start / End Time: 10:00 AM / 11:40 AM
Room: Astor Ballroom III, Astor, 2nd Floor
Presentation File: No File Uploaded


The first modern roundabout in the United States (U.S.) was built in Las Vegas in 1990. Since that time, the list of documented benefits of roundabouts has expanded while roundabouts themselves have been slow to diffuse. One place where roundabouts have not only gained favor but are now prioritized is Keene, New Hampshire (pop. 23,409). Keene is the first city in the U.S. to have evaluated all of its major intersections for roundabout conversion. As of 2017, there are five roundabouts in operation with another two in planning stages. In addition to enjoying the improved efficiencies of roundabouts, Keene has experienced environmental and health benefits as well. This research takes a before-and-after approach to assess how roundabout conversion of two of Keene’s highest volume intersections has impacted local air quality. Specifically, Particulate Matter 2.5 (PM2.5) is compared in the pre- and post-roundabout construction eras. Due to reduced idling and associated emissions reductions, PM2.5 levels were found to be significantly lower in the “with roundabout” time period. In addition, the proportion of the year identified as being “Unhealthy” or “Unhealthy for Sensitive Groups” was reduced by with 1.02-6.61 days per year after roundabout conversion. This research finds that roundabouts, particularly when installed at failing signalized intersections, can have air quality benefits that extend beyond the areas immediately adjacent to the intersection. This benefit may be more pronounced in communities with similar bowl-shaped topographies to Keene where pollutants tend to disperse within, rather than out of the area.

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