What Is a Road Diet?
The term sounds paradoxical at first: put a busy street on a road diet. But for a growing number of traffic engineers and urban planners, it represents one of the most cost-effective tools in modern city design. At its core, a road diet is a reconfiguration of a roadway that reduces the number of lanes dedicated to cars — typically transforming a four-lane road into three lanes, with two for through traffic and one center lane for shared left turns. The space gained is then repurposed for bike lanes, wider sidewalks, bus-only lanes, pedestrian islands, or green space.
Researchers and planners sometimes call this approach “right-sizing” roads, because it reallocates existing right-of-way to better support all transportation modes, including biking and walking. The first road diet in the United States was implemented in 1979 in Billings, Montana, and since then cities like Charlotte, Chicago, San Francisco, and New York have all embraced the model.
The Safety Data Is Hard to Ignore
The most compelling argument for road diets is the dramatic improvement in safety outcomes. The National Cooperative Highway Research Program (NCHRP) reported crash reduction rates of 19 to 47 percent in a study of 4-to-3 lane reconfigurations with a center two-way left-turn lane. These numbers align with real-world case studies from across the country.
After a road diet was completed on a 1.2-mile section of Seattle’s Stone Way North, crash data showed an overall decrease of 14 percent, injury crashes dropped by 33 percent, and angle crashes dropped by 56 percent. Bicycle volume increased 35 percent yet the bicycle crash rate showed no increase — and pedestrian crashes decreased by 80 percent.
New academic research reinforces this pattern. A 2023 study from the Johns Hopkins Bloomberg School of Public Health found that narrower lanes — nine, ten, or eleven feet — had lower accident risk compared to the standard 12-foot lanes recommended by transportation officials. The study analyzed 1,117 streets in seven cities and found that wider lanes with higher speed limits had significantly more crashes than narrower lanes.
Does Removing Lanes Cause Gridlock?
This is the question every skeptic asks — and the data offers a reassuring answer. Additional studies have shown that road diets often achieve positive safety effects without reducing traffic volumes. The key is applying them to the right roads.
When average daily traffic exceeds 20,000 vehicles a day, the safety gains can come with increased congestion and the possibility of diverting traffic to alternate routes. Below that threshold, however, the evidence is clear. On Armour Road in North Kansas City, Missouri, after a road diet that included protected bike lanes and pedestrian refuges, a before-and-after study showed a significant reduction in dangerous vehicle speeds, double the biking activity, and a negligible increase in travel times of around five seconds on average along the corridor.
What About Local Businesses?
Business owners are often the loudest voices against road diets, fearing that fewer lanes mean fewer customers. The evidence suggests the opposite. Road diets increase and enhance business activity by reducing traffic speeds — which helps motorists notice the shops and eateries they are driving alongside — and by accommodating pedestrians and cyclists, who tend to spend more money at local businesses than drivers do. Road diets often create more on-street parking spaces as well.
The results from Baton Rouge, Louisiana are a standout example. The Government Street road diet, which made the busy thoroughfare more pedestrian and bike-friendly, led to increased revenue growth at local businesses and reduced the number of traffic incidents on the street. In Fort Worth, Texas, when Magnolia Street was restriped with one lane each way and space dedicated to cyclists, restaurant revenue along the street jumped a combined total of 179 percent.
How Do Planners Choose Which Roads to Put on a Diet?
The large majority of road diet interventions involve converting four-lane undivided roads into three lanes. Many recent projects also utilize the extra space to add new bike lanes, sidewalks, on-street parking, wider shoulders, or concrete center islands. Planners typically prioritize corridors where traffic volumes fall within the safe range, where pedestrian and cyclist activity is suppressed by hostile conditions, and where crash histories signal a need for intervention.
Road diets are a popular tool for city planners to improve safety for bicyclists and pedestrians on high-capacity roads — and often at low cost. Signal optimization is another key ingredient: one study showed that signal optimization along traditional four-to-three lane road diets can mitigate the effects of delay resulting from capacity reduction.
The Political Challenge
Despite the successes, road diets often face pushback. Residents worry about increased travel times, emergency vehicle delays, or reduced access to local businesses. But with data-driven planning and community engagement, many of these concerns can be addressed — or even reversed.
Since road diets often face resistance, quantifying the success of past road diets and showing how traffic impact will be measured can help answer constituent concerns around travel time impact. Transparency, early community involvement, and clear before-and-after metrics are the hallmarks of projects that become success stories rather than controversies.
The Bottom Line
Road diets challenge a deeply ingrained assumption: that more lanes equal more mobility. The data consistently shows that right-sized roads move people more safely, support local economies, and open the door to greener, more human-scale city streets. Road diets provide the opportunity to turn high-speed, low-capacity streets into vibrant corridors — and in an era of rising traffic fatalities and car-dominated urban sprawl, that opportunity is increasingly hard to ignore.
