European-style traffic roundabouts, like this one in Reno, are not only civilized and safe(r), they are good for the environment.

A study found that they generate half the vehicle emissions of intersections controlled by traffic lights.

Tom Vanderbilt, the author of Traffic, explains that the “most obvious” reason is that “a stopped vehicle generates on the order of seven times the emissions of a vehicle moving at 10 miles an hour.”  That wasn’t necessarily obvious to me (in fact I had not clue this would be the case), but good to know!