A road diet is a reduction in the number of general-purpose traffic lanes, or in lane widths, on a road or street. Road diets often involve converting an existing four-lane street into a three-lane street consisting of two through lanes and a center lane for left turns.
Among the most important benefits of road diets is reduced local air pollution, resulting from the reduced number of vehicles using the road. Another benefit is improved safety for pedestrians because of the usually widened sidewalks and the reduced width of the street to be crossed. Safety can also be increased for bicycle riders by the addition of protected bicycle lanes. The local quality of life is often further enhanced by the addition of trees or other landscaping.