road diet
n. A reduction in the number of travel lanes available on a road, usually by converting one or more existing travel lanes into turn lanes, bike lanes, or street parking.
Other Forms
No offense to Kensington Avenue, but the road could use a little slimming down.

At least that’s the thinking of the Town of Amherst, which is prescribing a "road diet" for the one-mile stretch of Kensington, between Main Street and Harlem Road.

Of course, in this case, a diet actually means restriping the county-owned road to reduce the number of travel lanes. That’s expected to lower the speed of the traffic, while opening up the possibilities of adding bicycle lanes and street parking.
—Jay Rey, “'Road diet' prescribed for Kensington Avenue in Amherst,” The Buffalo News, April 29, 2015
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.
—Eric Jaffe, “So What Exactly Is a 'Road Diet'?,” City Lab, September 12, 2014
Road diets have long been practiced in Europe and are more popular in peer cities like San Francisco and Seattle. The idea seems to be gaining favor among Portland transportation planners, though they're sometimes wary of using the "road diet" term.
—Steve Law, “City hopes 'road diet' improves livability,” Portland Tribune, August 15, 2013
1999 (earliest)
Road dieting is a new term applied to skinnying up patients (streets) into leaner, more productive members of society. …

Burcham Road in East Lansing, Michigan, was formerly a fat road. Speeds were excessive. Pedestrians near the high school found it unsafe to cross the four-lane roadway. Neighbors complained about noise and danger. East Lansing's traffic engineer, John Matusik, P.E., felt that this roadway was a prime candidate for a road diet.
—Dan Burden & Peter Lagerwey, “Road Diets: Fixing the Big Roads” (PDF), Walkable Communities, March 15, 1999
Road Diet: Travel lanes replaced by a bike lane and parking. Source: Eric Fredericks (Flickr).