Abstract
All-red and yellow clearance intervals are closely related to traffic crashes at intersections. In 1998, Sacramento County DOT retimed the clearance interval throughout the county. Crash and traffic volume data were obtained from Sacramento County. The before-and-after evaluation of the impact on crash rates was conducted in this project. Two sets of data were analyzed. Fifty-nine intersections with crash and traffic volume data, along with eighteen intersections along major corridors with crash data and approximated traffic volumes, were analyzed. It was found that extending yellow time and adding an all-red clearance interval can be effective in reducing injury and fatality rates. Total collision rates were also reduced as a result of these signal timing changes.