Abstract
The delay to a platoon of traffic at an unsaturated signal is examined. The departure rate in the green period is assumed constant as long as there is a queue at the signal, but the arrival rate is allowed to vary along the platoon. The delay is expressed in terms of the forms and duration of the platoon and the arrival time of the leading vehicle (relative to the beginning of the signal cycle). Two analytical expressions cover all the possible case. A single expression is found for the rate of change of the delay per cycle with to the arrival time of the leading vehicle; this rate of change is expressed in terms of observable quantities and a practical application of the formula is suggested.