A road diet changes roadway usage by replacing some of the typical traffic lanes to make space for other uses like bicycle lanes, sidewalks, or parking.
A road diet reconfigures a roadway by replacing some of the typical vehicle-based traffic lanes with other uses, such as bicycle lanes, sidewalks, or parking.
One of the most common road diet configurations is the conversion of a four-lane undivided roadway to a three-lane roadway made up of two through lanes and a center two-way left-turn lane.
The lane reduction provides new space for one or more of the following additional services:
- Bicycle lanes to encourage people to bike on the corridor or primary roadway, and protect bicyclists from vehicles
- Sidewalks to encourage pedestrians to walk along a primary roadway
- Pedestrian refuge islands in the middle of the roadway to help people cross the street safely
- Transit-related facilities like bus pullouts and enhanced bus shelters
- Parking to increase vehicle access to businesses and residences along the corridor
- Placemaking items like vegetation, illumination, and other aesthetic treatments
The objectives of road diets may include improving safety, reducing speeds, improving pedestrian and bicyclist accessibility, or enhancing transit stops. Identifying specific objectives can help an agency determine if a road diet will be an effective strategy.
When to use this strategy
Road diets make sense for urban and suburban roadways with excess capacity and a history of collisions related to turning vehicles—especially left turns at driveways between intersections.
One of the most common applications of road diets is on four-lane, undivided roads that experience increased incidents as traffic volumes increase. In particular, rear-end, sideswipe, and left-turn collisions tend to increase four-lane, undivided roads, as do conflicts involving pedestrians or bicyclists, and road diets can provide much needed solutions.
Reducing from a four-lane roadway to three lanes (two through lanes and a center two-way left-turn lane) can provide significant benefits for multiple road user types and reduce different kinds of collisions.
A Road Diet improves safety by adding a protected left-turn lane for mid-block left-turning drivers, reducing the crossing distance for pedestrians when refuge islands are added, and reducing vehicle travel speeds. Road diets have been shown to reduce collisions by 17 to 47 percent.
There are often concerns about reducing the capacity of a four-lane, undivided roadway to 50 percent by removing two through lanes with a road diet. But agencies have found that, typically, a four-lane, undivided roadway is not operating efficiently due to left turns and widely varying speeds. As a result the travel time through the corridor is often the same, or even lower, once the road diet has been implemented.
A road diet can improve bicyclists’ and pedestrians’ access along the corridor or primary route by including bicycle lanes and pedestrian improvements. In addition, slower vehicle speeds can improve comfort for people who walk or bike.
Many road diets can be implemented with no additional pavement added. The reconfiguration is as simple as removing and replacing striping, and changing some signage. Traffic signals may also need to be moved on their existing mast arms or overhead wires to match the new lane locations.
What you need in order to implement
- In some jurisdictions, maintenance funding is tied to the miles of vehicle lanes, so reducing the number of lanes can have an unintended, negative impact on maintenance budgets. Agencies should coordinate with their funding sources to ensure road diets do not reduce maintenance funds.
- For more complex road diets that require property purchases and/or new pavement, the project will need to go through a typical planning process that includes public feedback and environmental study.
- Buses, mail service, and delivery trucks sometimes block one of the two lanes of a four-lane, undivided roadway, forcing approaching vehicles to go around. When an agency removes that second lane in each direction by implementing a road diet, it is important to coordinate with the transit agencies, mail delivery, and other delivery services to identify proper parking locations for their required stops. For example, a special area designed for the bus to pull into or Bus Only parking along the curb can help buses travel along a road diet.
- As an innovative treatment, road diets can be misunderstood by the public who think they are losing part of their roadway. Agencies should create a public awareness campaign and coordinate with nearby businesses, residents, and travelers to share the benefits of road diets, as well as address any concerns.
- Typical signing, stripe removal, and striping equipment will be necessary for installation.
- Normal maintenance that includes addressing roadway issues like potholes, restriping the lane markings, and sign upkeep.
Agency resources needs:
- Staff to plan, design, construct, and maintain the road diet, or funding to hire outside of the Agency for one or more of these services.
Learn more about this strategy
Federal Highway Administration Road Diet Resources Website.
Federal Highway Administration Road Diet Informational Guide, FHWA-SA-14-028, Washington, DC, 2014.
Federal Highway Administration Road Diet Case Studies, FHWA-SA-15-052, Washington, DC, 2015.
Federal Highway Administration Road Diet FAQ, FHWA-SA-17-021, Washington, DC, 2017 (PDF).
(1) FHWA "Evaluation of Lane Reduction 'Road Diet' Measures on Crashes." FHWA-HRT-10-053. (Washington, D.C: 2010)
About key characteristics
Road diets can be installed in a variety of locations, including rural areas. They are most common when reconfiguring urban and suburban undivided roadway corridors.
Costs can be low as basic road diets can be installed using only traffic paint to apply new lane markings on roads.
Road diets reconfigure the roadway, so the technology needs are quite low. Sometimes traffic signals may need to be retimed due to the new lane configurations.
On some corridors a road diet is a major change for the traveling public, so agency staff should reach out to all involved stakeholders to share and provide education about the benefits.