Additive measures of travel time variability

This paper derives a measure of travel time variability for travellers equipped with scheduling preferences defined in terms of time-varying utility rates, and who choose departure time optimally. The corresponding value of travel time variability is a constant that depends only on preference parameters. The measure is unique in being additive with respect to independent parts of a trip. It has the variance of travel time as a special case. Extension is provided to the case of travellers who use a scheduled service with fixed headway.

► We model travellers with explicit scheduling preferences at origin and destination.
► Travellers choose departure time minimising the expected cost of random travel time.
► We seek variability measures additive in respect to independent parts of the trip.
► The cumulant generating function and the variance are the only additive measures.
► The value of variability depends only on the scheduling preferences.