UCLA Institute of Transportation Studies

Los Angeles has adopted a “Vision Zero” policy to eliminate, or at the very least meaningfully reduce, fatal and severe traffic collisions. A road diet, also known as a “lane reconfiguration”, consists of converting vehicle travel lanes to other uses in order to serve safety or transportation-related goals. It is a tool that can help achieve the Vision Zero policy goal by discouraging speeding and reducing risky lane changes to improve road safety. This report studies the safety impacts of high ADT road diets to determine whether the existing 20,000 ADT threshold should be revisited. I compared collisions and speeds on five high ADT road diet corridors to 16 similar multi-lane, untreated streets segments in Los Angeles. Collision rates in the high ADT road diet corridors were 44% lower than in the comparison corridors. Fatal injuries were 200% lower and severe injuries were 37% lower. The average vehicle travel time for the comparison corridors was only about 11 seconds faster than in the road diet corridors. Thus, I recommend for the city to consider revisiting the ADT threshold guidelines for road diets in order to implement more high ADT road diets though city initiatives to improve road safety.