UCLA Institute of Transportation Studies

This capstone evaluates the effectiveness of three residential intersection treatments, all-way stop control, neighborhood traffic circles, and mini-roundabouts, in reducing vehicle speeds, a key factor in traffic safety. In response to growing cut-through traffic on residential streets and the City of Los Angeles’ efforts through Vision Zero and the Mobility Plan, this study combines a literature review with a before-and-after analysis of 33 intersections across the city using weighted averages and paired t-tests. Results show mixed outcomes for all-way stop conversions, with some intersections showing reduced speeds and others showing little change or increases, likely due to limited driver compliance. Neighborhood traffic circles, on the other hand, consistently reduced both average and 85th percentile speeds, especially at locations with greater physical deflection, confirming their effectiveness as a traffic calming tool. Mini-roundabouts, while promising in the literature, showed modest results in this study due to a limited sample size. Overall, the analysis finds that physical design features, such as center island size and narrower travel paths, more reliably slow traffic than signs and paint alone. Based on these findings, the capstone recommends coupling all-way stops with midblock treatments, expanding the use of traffic circles with improved geometric design, and piloting additional mini-roundabouts on higher-volume Neighborhood Enhanced Network corridors. These strategies can help Los Angeles retrofit its residential streets to reduce vehicle speeds, improve safety, and better support walking and biking, especially in neighborhoods facing growing traffic impacts from cut through drivers.