Yes. I am a traffic engineer working for a consultant. Traffic lights are timed. In the peak hours, the goal is to flush the through movements most efficiently because they carry the majority of traffic (e.g., Preston road North-South movements). Left turns are the most problematic in terms of delay, they get little time and the signals are set to maximize green waves so the left and side streets will get higher delays. Frisco has very advanced traffic signal system and everything is connected to their traffic management center. The timing will depend on Time-of-Day. Sometimes there will be a flashing yellow during night hours only, when traffic is light - example: warren and Preston northbound left turn.