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. a photo of a tiny house in Oregon
    Design

    How Amazon Could Transform the Tiny House Movement

    Could the e-commerce giant help turn small-home living from a niche fad into a national housing solution?

  2. The downtown St. Louis skyline.
    Perspective

    Downtown St. Louis Is Rising; Black St. Louis Is Being Razed

    Square co-founder Jack Dorsey is expanding the company’s presence in St. Louis and demolishing vacant buildings on the city’s north side.

  3. an aerial view of Los Angeles shows the complex of freeways, new construction, familiar landmarks, and smog in 1962.
    Transportation

    The Problem With Amazon’s Cheap Gas Stunt

    The company promoted its TV show The Marvelous Mrs. Maisel with a day of throwback 1959-style prices in Los Angeles. What could go wrong?

  4. Warren Logan
    Transportation

    A City Planner Makes a Case for Rethinking Public Consultation

    Warren Logan, a Bay Area transportation planner, has new ideas about how to truly engage diverse communities in city planning. Hint: It starts with listening.

  5. Environment

    What U.S. Cities Facing Climate Disaster Risks Are Least Prepared?

    New studies find cities most vulnerable to climate change disasters—heat waves, flooding, rising seas, drought—are the least prepared.

×