The concept of delay

The word delay is so widely used that it may be assumed to be a simple concept which is well understood. It is taken to be a name for wasted time on a journey, but attempts to quantify it in order to use it as a measure of performance of a transportation facility have not given complete satisfaction. Drivers are observed to behave in ways which reveal attitudes to wasted time which differ from those of the researcher. These problems have been reported in many studies but do not seem to have been pursued.This paper discusses the concept of delay. A basic definition leads to problems of measurement which suggest alternative definitions which have more apparent relevance to traffic networks in which more than one cause of delay is of interest. Further speculation about these definitions points to the fact that delay can be either of two separate concepts.In conclusion it is argued that delay should no longer be regarded as an objective quantity capable of direct measurement. Instead of delay being thought the cause of driver annoyance, it should be taken that it is the existence of driver frustration which converts time lost into delay. It is better to define delay as unwanted journey time.