Research Lead: Dylan Jouliot
UC Campus(es): UCLA
Problem Statement: While numerous studies have shown road diets can greatly reduce the number and severity of collisions, especially for pedestrians and cyclists, the public response to many of the changes implemented in Los Angeles has been quite negative. Angry residents and commuters have organized protests of the roadway changes, initiated campaigns to recall city councilmembers who have supported the changes and even successfully lobbied to have road diets undone and converted back to their previous state. This negative response has largely centered on claims of large increases in congestion and travel times along the streets where the Los Angeles Department of Transportation (LADOT) has removed lanes.
Project Description: The Active Transportation and Special Programs (ATSP) team of the Southern California Association of Governments (SCAG), the Metropolitan Planning Organization for the Southern California region, has a strong interest in improving traffic safety in the region, and seeks research to determine if these proven safety improvement measures cause the delays and increases in congestion that opponents claim. To examine this issue the graduate student researcher surveyed existing literature on road diets and their congestion impacts, analyzed before and after LADOT daily traffic volume data for a number of street segments where the city installed road diets and nearby parallel segments where no change was made, and observed current conditions of ten intersections within the selected street segments to assess potential ongoing delay and congestion in the study corridors. The analysis finds an overall increase in traffic volumes on the selected road diet corridors of 8 percent, while volumes decreased very slightly on nearby parallel corridors. While the limitations of using daily traffic volume data to estimate congestion mean that these results do not disprove the possibility of increased congestion after road diet installations, the fact that more vehicles passed through road diet corridors without corresponding increases in volumes on nearby streets suggests that drivers did not divert to nearby streets as might be expected with increases in congestion and delay. Field observations of representative intersections for each of the four road diet corridors and their respective control corridors suggest that current lane configurations have not negatively affected peak-hour traffic flow or level of service on either the road diet or control corridor.