So What Exactly Is a 'Road Diet'?

Earlier this week, the U.S. Department of Transportation announced an 18-month campaign to improve road safety across the country. One of the things DOT plans to do is create a guide to "road diets" that it will distribute to communities and local governments. DOT says that road diets can reduce traffic crashes by an average of 29 percent, and that in some smaller towns the design approach can cut crashes nearly in half.

But what exactly is a road diet? A good place to start is the apparent source of DOT's safety figures: a 2013 white paper on road diets prepared for the Federal Highway Administration by Libby Thomas of the University of North Carolina Highway Safety Research Center. While road diets have been around for decades, writes Thomas, it's only in the past 10 years or so that experts have understood just how beneficial they can be: