How is the length of yellow time calculated for traffic signals?
The City of Roseville follows both Federal and State guidelines, the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD), and the MUTCD California Supplement. The length of yellow time for through traffic movements are based on approach speeds (the 85th percentile speed from radar speed surveys). Longer yellow times are appropriate for through lanes with higher approach speeds. Vehicles making left turns typically have much slower approach speeds than that of through traffic lanes. The MUTCD California Supplement Table 4D-102 suggests minimum yellow times of three seconds. A three second yellow is typically used in left turn movements throughout the State of California. A common misconception is to assume yellow time is clearance time to get through an intersection. However, Section 4D.10 of the MUTCD states that the exclusive function of the yellow change interval is to warn traffic of an impending change in the right-of-way assignment. In other words, the purpo
