A three-objective user equilibrium model:Time surplus maximisation under uncertainty

In this paper, we propose a user equilibrium model considering the three most important factors influencing route choice behaviour in a road network, namely, travel time, travel time reliability and monetary cost. We further develop the time surplus maximisation bi-objective user equilibrium (TSmaxBUE) model and incorporate the concept of travel time budget to model how users might react to uncertainty induced by day-to-day variability in travel time caused by traffic incidents. This results in a three-objective user equilibrium model, which has a possibly infinite set of equilibrium flows. To compute equilibrium flows, we introduce time budget surplus (TBS) defined as the maximum travel time a user is willing to spend minus the actual time budget required for a desired level of travel time reliability. At equilibrium, for each origin-destination (O-D) pair, all individuals are travelling on the path with the highest TBS value among all the efficient paths between this O-D pair. This becomes a time budget surplus maximisation three-objective user equilibrium model (TBSmaxTUE). We show that the TBSmaxTUE model is a special case of three-objective user equilibrium considering minimisation of expected travel time, travel time variance and toll (monetary cost) as objectives. We illustrate the model and our results on a small network