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Imagine you are hired by a municipality for a streetscape project to enhance the look and function of a busy corridor. It’s a four-lane undivided highway that has recently seen an uptick in vehicle and pedestrian accidents. Some quick research shows this stretch of road connects to others with established bike lanes, though there are none here. You suggest a road diet and get a blank look from the client. A road what? Let’s explain.

A road diet can be thought of as a roadway reconfiguration, or repurposing lanes within the existing footprint, to provide additional roadway features that can enhance the use and improve the safety of the corridor. The most common example of a road diet project consists of the conversion of a four-lane undivided roadway to a three-lane section of roadway, consisting of one through lane in each direction and a center two-way left turn lane or center median with left turn lanes. For this type of reconfiguration project, the existing road pavement space can be repurposed to provide other features to the corridor, such as center turn lanes, a median, bike lanes, on-street parking, bus pullouts and wider sidewalks. These features associated with the road diet conversion can improve safety, allow allocation of road space for other multi-modal users, and provide support for economic enhancement along the corridor.

Highway Before and After Road Diet

Safety Improvements Road diets have been shown to provide safety improvements on corridors that have a history of high crash rates. An example we might see is a four-lane undivided highway with a high density of driveway access and minor street intersections. In this scenario, the inside through lanes often act as de facto left turn lanes, which can lead to high rates of rear end, side swipe and high impact angle collisions. A center turn lane can separate the left turning traffic from the through traffic, helping to reduce collisions and improving sight lines for making left turn maneuvers. The road diet design features with reduced lane widths, center medians, wide sidewalks, enhanced landscaping, etc. can also create a feeling of lower operating speeds to drivers which can naturally reduce speeds within the corridor. The road diet can also improve safety for pedestrians by reducing the number of lanes required for crossing the road and providing wider sidewalks and median islands which can act as pedestrian refuges.

Multi-Modal Benefits There are also benefits of enhanced multi-modal use of the corridor associated with a road diet. The road space can be reallocated among the various types of multi-modal road users to help provide a balance of the users throughout the corridor. Examples of multi-modal enhancements include the addition of bike lanes, wider sidewalks, median refuge islands for pedestrians, bus pull-outs and queue jump lanes, and on-street parking.

Economic Benefits Features of a road diet project can also help contribute to the economic enhancement of a corridor. Wider sidewalks provide a more walkable setting and can help increase pedestrian activity at the store frontage of local shops, restaurants and businesses. A left turn lane and on-street parking can provide easier and more convenient access to businesses. On-street parking can also provide better access for deliveries. The overall feel of the corridor with wider sidewalks, increased landscaping and reduced corridor speeds help to provide a more inviting area that can generate more pedestrian and customer activity.

Traffic Efficiency A common argument against road diets is that removing lanes for vehicles will make traffic worse, because capacity has been reduced. This is not necessarily the case. As we see in the scenario of the four-lane undivided section, where the inside lanes operate as de facto left turn lanes, the roadway segment essentially already operates as a three-lane road section.

A road diet may not be feasible in every situation. The designer will need to evaluate if the enhancement features of the road diet (safety benefits, improving multi-modal use and support of potential economic enhancement) can be achieved without having negative impacts on standard traffic operations of the corridor. The road diet can be a relatively low-cost project that can improve safety features of a corridor, provide balance of multi-modal users of the road space and support potential economic enhancement in the area.

Back to the client – you see the light bulb go off. Increased traffic efficiency, safety, and economic benefits? This is a diet with a lot to add to your project!

About Stevie Berryman, PE

Stevie Berryman, PE is a Project Manager for Foresite Group’s Traffic Engineering Division in Peachtree Corners, GA. Stevie graduated from the Georgia Institute of Technology with a Master’s degree in Construction Management. In his spare time, Stevie is a coach for a youth travel baseball program.


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