Why the Light Turned Green and You Still Didn't Make It Through

You are third in line at a red light. The signal turns green, the cars ahead take a beat to roll, and by the time your bumper reaches the stop bar, the light is already turning yellow and trapping you for another cycle. Nothing in the signal controller failed—you just watched a time budget run out. This video breaks down the street-level arithmetic of traffic signals and intersection capacity. A green light is permission to move, not a guarantee of room. Once you account for start-up lost time at the front of the queue and yellow-plus-red clearance lost time at the back—commonly approximated at four seconds per phase—the 'effective green' is a service duration that differs from what the lamps display. We trace how engineers slice a fixed hour among competing movements, why skewing an intersection's angle stretches pedestrian crossing times, and why a movement running below capacity on paper can still fail on individual cycles when a slow truck or a hesitant driver tips the clock over. Finally, we look at how those leftover vehicles become residual queues, why sizing turn bays for the average queue instead of the 95th-percentile queue lets waiting cars spill out, and how to count the seconds of a green light yourself the next time you are waiting in line. 0:00 The Green Light That Doesn't Move 1:33 Effective Green and the Four-Second Loss 5:20 Lanes, Skew Angles, and Pedestrian Claims on the Clock 7:07 Critical Movements and the Fixed Hour 8:35 Why a Cycle Fails Even Below Capacity 11:36 Four Cars Cost Ten Seconds: Queue Arithmetic 12:44 The 95th-Percentile Tail and Spillover Queues