A road diet is generally described removing vehicle lanes from a road to allocate extra space for other uses such as parking, sidewalks, bicycle lanes, and turn lanes. The main purpose of a road diet is to improve pedestrian and traffic safety, and they can be relatively low cost if planned correctly. The Federal Highway Administration published a road diet case studies guide with 24 case studies highlighting the implementation of Road Diet plans in the United States. Each case study contains information on the objective, features, and results of the road diet plan, along with various maps and photos of the streets in the area. For most of the plans, the main objective is to reduce traffic congestion and to improve safety of pedestrians and cars. The results have been generally positive with examples such as reduction in crashes, reduced speeds, and improved bicycle experience.
More resources from the federal government regarding road safety design includes the Federal Highway Administration's Road Diets website