Developing a Safe System Approach to Setting Speed Limits

Over the last decade in California there has been a surge in the number of traffic fatalities, with especially large increases in pedestrian fatalities. At the same time, the California Department of Transportation (Caltrans) has affirmed a vision of reaching zero fatalities and serious injuries on state highways by 2050 and has committed the department to reaching this goal by adopting the Safe System Approach. The Safe System Approach is underpinned by the principles that humans make mistakes and that the transportation system should be designed to account for the human body’s ability to tolerate crash impacts. Because speed increases both the likelihood of being involved in a crash and the severity of injuries sustained in a crash, speed management is critical to designing a Safe System for all road users. In contrast to a Safe System Approach, in which speed limits are set in a manner that minimizes the risk of serious injury or death, the current approach to speed-limit setting in California is based on driver behavior (using the 85th percentile rule). This report builds off research and case studies within and outside of the United States to provide a framework for the State of California to develop a new roadway-based, context-sensitive approach to establishing speed limits that prioritizes the safety of all road users.