Development of comprehensive level-of-service criteria for the maintenance of traffic light signals. 1.: System requirements.

This is the first of three papers detailing the development of traffic signal maintenance objectives. The criterion developed is the fraction of traffic signals defective with faults which cause "unacceptable" delay. This concept of "unacceptable" delay is related to a delay threshold above which motorists exhibit behaviour (e.g. creeping forward at traffic signals) which shows that they have recognised faulty operation, and may be contemplating unsafe actions.