Planner Jeff Speck leads a video tour of four different street redesigns.

Jeff Speck: Four Road Diets from Cupola Media on Vimeo.

A road diet is a great way for cities to reclaim some of the excess street space they’ve dedicated to cars—generally preserving traffic flows while improving safety and expanding mobility to other modes. But just as food dieters have Atkins, South Beach, vegan, and any number of options, road diets come in many flavors, too. Urban planner and Walkable City author Jeff Speck, in collaboration with graphic artist Spencer Boomhower, takes us on a tour of four types of street diets in a deliciously clear new video series. Here’s a taste.

Three lanes to two

(Jeff Speck / Spencer Boomhower)

In this case we have three traffic lanes flanked by two parking lanes. That’s an awful lots of city street space for cars, so here Speck proposes a “3-to-2” road diet: by removing one traffic lane and narrowing one parking lane, a city can make room for a protected two-way cycle track beside the curb. The 3-to-2 diet preserves travel times while increasing safety; as Speck point out, a similar design change made in Brooklyn reduced injury crashes by 63 percent.

Four lanes to three

(Jeff Speck / Spencer Boomhower)

The most classic road diet converts four lanes of traffic into three lanes: one in each direction, plus a left-turn lane in the middle. By eliminating one full car lane, the “4-to-3” diet also leaves room for bike lanes on both sides of the street—though this extra space can be used for sidewalk extensions or even dedicated transit lanes, too. A 2013 study of 4-to-3 diets found major safety benefits: a 47 percent drop in crashes in small metros, and a 19 percent dip in big cities.

Bike lanes to cycle tracks

(Jeff Speck / Spencer Boomhower)

"Bike lanes are good; a cycle track is better, and requires no more roadway,” says Speck in the road diet’s voiceover. Take the road that we ended up with after the 4-to-3 diet, for instance. In this design, bike lanes run beside car traffic on either side of the street, increasing the potential for collision. But by sliding one parking lane off the curb, this diet makes room for a two-way cycle track protected from moving traffic by a buffer strip as well as a lane of street parking.

40-footer lane insertion

(Jeff Speck / Spencer Boomhower)

This time we focus on a 40-foot street with two 12-foot lanes of opposing traffic and two parking lanes at the curb. Many cities have adopted 12-foot lanes with the assumption that they move more traffic; in fact, as Speck has argued at CityLab before, they present a major safety hazard for cities by encouraging faster driving. He recommends slimming them down to 10 feet—a design configuration that leaves room for a bike lane and makes the street safer, even as it more or less preserves traffic flows.

About the Author

Most Popular

  1. Passengers line up for a bullet train at a platform in Tokyo Station.
    Transportation

    The Amazing Psychology of Japanese Train Stations

    The nation’s famed mastery of rail travel has been aided by some subtle behavioral tricks.

  2. Transportation

    Madrid Takes Its Car Ban to the Next Level

    Starting in November, the city will make clear that downtown streets are not for drivers.

  3. Maryland Governor Larry Hogan signs bills for Metro funding and Amazon incentives in Rockville on April 25.
    Life

    Why Do Politicians Waste So Much Money on Corporate Incentives?

    Political scientist Nathan Jensen answers questions about his new book, Incentives to Pander.

  4. A sign for women-first parking in a Seoul shopping center.
    Life

    What’s Up With Seoul’s Pink Parking Spaces for Women?

    They’re like regular parking spaces. Except, you know, pink.

  5. Occupy Wall Street protesters rally in Canal Street in Lower Manhattan in November 2011.
    Life

    How Centuries of Protest Shaped New York City

    A new book traces the “citymaking process” of riots and rebellions since the era of Dutch colonization to the present.