Yellows lights are 3-4 seconds long. In Cali, if you get a yellow you better damn STOP because red is one second away.
Signal timing is designed to meet changing travel patterns and distinct intersection characteristics. Signals can be: preset timing, semi-actuated, and fully actuated. The phase intervals are based on certain parameters such as: change period, perception and reaction time, speed on approach, deceleration rate, grade and conditions, width of intersection, and vehicle size.
California MUTCD guidelines are 3-6 seconds yellow with red clearance intervals no longer than 6 seconds. Most red clearance intervals at .5 to 2 seconds.
If you’re seeing one second yellows commonly then it’s a head scratcher.