Traffic engineers hate left turns because they slow everybody down and are dangerous to boot. Solutions such as dedicated lanes or routing traffic over intersections don't truly solve the problems. What to do? Slate takes a look at an emerging idea called the "diverging diamond interchange," which eliminates left turns altogether. The first one in the US went up in 2009 in Springfield, Missouri, and others are now in the works.
Tom Vanderbilt takes a crack at explaining: "As the eastbound driver approaches the highway interchange (whose lanes run north-south), traffic lanes 'criss cross' at a traffic signal. The driver will now find himself on the 'left' side of the road, where he can either make an unimpeded left turn onto the highway ramp, or cross over again to the right once he has gone under the highway overpass." (See the video in the gallery for a simulation.) Sounds convoluted, but drivers apparently haven't had much trouble catching on. Click for the full column for details, including possible drawbacks. (Read more Federal Highway Administration stories.)