4- to 3-Lane Conversions

A 4- to 3-lane conversion, also called road diet, is when an existing roadway is reconfigured to add a center turn lane. The primary benefits are enhanced traffic safety, mobility and access for all road users and a "complete streets" environment to accommodate a variety of transportation modes.

Primary BenefitsRoad diet before and after (no bike lanes shown)

  • Crash Reduction - Decreases left-turn, rear-end and side-swipe crashes due to the dedicated center turn lane. 
  • Reclaimed Space - Extra space can now be used for enhancements like landscaping, green infrastructure, parking, bike lanes, bus stops, etc.
  • Improved Walkability - There are fewer lanes for pedestrians to cross and traffic is located farther from the sidewalk.
  • Traffic Calming - Regulates speed, creating more consistent traffic flow.
  • Easier Access - Easier to access homes, schools and businesses. More comfortable for vehicles on side streets trying to enter main roadway, particularly for left turns because there are fewer traffic lanes to clear while turning.

Lane Conversions in Royal Oak


E. Fourth Street

The city converted this boulevard street from two lanes to one lane in each direction, with buffered bike lanes along the outside of the roadway. This is one of the most used bicycle routes in the city.


N. Main Street

The city installed by north-south bike route on N. Main Street by implementing a road diet from Euclid Avenue to the north city limits. Main Street was reduced to one lane for north-south travel with a center turn lane. Six refuge islands were installed along the corridor to provide safer crossings for pedestrians.

S. Campbell Road

The city implemented a road diet on S. Campbell Road from 10 Mile Road to E. Fourth Street, that added bike lanes and  two pedestrian refuge islands to create safer crossings near Oakland Elementary and VFW Park.


Rochester Road

Rochester Road from N. Main Street to 13 Mile Road was converted to a three lane roadway when it was resurfaced. The curbing was moved inward to provide more greenspace and the city made several additional improvements by adding public on-street parking stalls adjacent to Wagner Park, installing pedestrian crossing islands near Wagner Park and La Salle Avenue, and creating rain gardens to increase green infrastructure on the west side of the roadway near Dewey Street, Wagner Park, and Linden Avenue.

Common Misconceptions

Do road diets lead to slow emergency response times?

Road diets can significantly improve response times by allowing emergency vehicles to bypass traffic by using the center turn lane. 

Do road diets make traffic worse?

No, the majority of through traffic will tend to use the outside lanes to avoid being delayed by left-turning vehicles slowing and stopping in the inside lanes. The corridor essentially operates like a three-lane road, so when they are converted to a three-lane section they are unlikely to experience a change in capacity. Studies show improved operation and safety because left turns are shifted to the center turn lane, allowing traffic to flow more freely in the through lanes. Before implementing, it is important to study the traffic patterns and capacity of the road to ensure that a lane conversion will not cause traffic backups.

Do road diets increase driveway and side street delays?

Vehicles on side streets can more comfortably enter the main roadway because there are fewer lanes to cross. This can also reduce delays exiting side streets. Road diets reduce speeds, and creates more consistent traffic flow and less stop-and-go traffic.

Drivers will be diverted to other streets.

For the majority of road diets, traffic volumes remain about the same through the corridor. Drivers tend to take different routes when there are traffic backups. Road diets are only recommended when the new configuration can handle the traffic flow without major backups. In addition, three-lane roads are generally more efficient as vehicles no longer need to stop in the through lane to make left turns.

Three Is Better Than Four

Iowa Road Diet video thumbnail Opens in new window

The Iowa Department of Transportation put together an educational video providing information and graphics to help describe and illustrate the benefits of 4- to 3-lane conversions. Click the thumbnail to watch the video on YouTube.