Theoretical threshold of travel time for travel time reliability from probabilistic measures

Travel time threshold is a key parameter for calculating the travel time reliability (TTR) of a road network from probabilistic measures. However, the lack of an accepted criterion has been a barrier for TTR to be applied extensively. To develop an acceptable criterion, this research defined the travel time threshold, presented an optimisation model of traffic operation efficiency, and found the value range by solving this model. A utility model of traffic operation efficiency to the travellers' benefits and a utility model of travel time to travellers' costs were developed. An equilibrium model was constructed by considering the trade-off between the relative change rates of these utilities. The equilibrium model was solved to obtain the quantified results. This theoretical method balances the traffic operation efficiency and travellers' travel costs simultaneously. Simulation test results show the reasonability and the applicability of the travel time thresholds.