Lost time is the time, in seconds, during which an intersection is not used effectively by any movement. For any signalized intersection phase where one or more traffic movements are initiated, lost time is generally considered to be equivalent to the sum of the yellow plus all-red intervals at the end of the phase.

The figure above illustrates how the start-up delay component of lost time occurs at a signalized intersection. Start-up lost time is the additional time, in seconds, consumed by the first few vehicles in a queue at a signalized intersection above and beyond the saturation headway, because of the need to react to the initiation of the green phase and to accelerate. The bottom graphic illustrates a typical distribution of headways that might be observed for successive vehicles as they discharge from the stop line at the beginning of the green interval. The difference between the minimum sustainable headway, h, and the observed headway (shown as a red point) represents the portion of the start-up delay incurred by that particular vehicle. Taken together, the sum of the e(i) values equals the start-up delay.