In 2023, Keene, a small college town with about 23,000 residents, installed its seventh and newest roundabout. These circular intersections are easily confused with rotaries or traffic circles, but are distinctly free of traffic lights. Instead they require drivers to yield to traffic before entering and are constructed to be slower-moving while minimizing stopping.

These features make modern roundabouts significantly safer than other intersections. Because of the position of the cars, they can drastically reduce the chances of potentially deadly crashes, like T-bones or head-on collisions. And because cars can generally keep moving without idling at red lights, they also burn less gasoline.

This means each vehicle spends less time pumping out planet-warming pollutants, like carbon dioxide. Installing roundabouts also improved Keene’s air quality, which used to rank among the worst in New England. In a study published in 2018, a former Keene city planner found soot and other small airborne particulates, which can be harmful to human health, had fallen by up to 40 percent.