A Whole-Link Travel-Time Model with Desirable Properties

In network models for dynamic traffic assignment the link travel times are often describedby “whole-link ” models. In particular, they have been expressed as a function of the num-ber of vehicles currently on the link. Such whole-link models are useful approximations and make the network model tractable when flows and travel times are varying over time. Here we propose an alternative whole-link model to approximate travel times. For a vehicle enter-ing a link at time t, we let the link travel time be a function of a weighted average of the inflow rate at the time it enters and the outflow rate at the time it exits. We show that this model ensures first-in-first-out and has other desirable properties. We indicate computational methods for solving the model, apply it to various patterns of inflows, and compare the numerical results with two alternative whole-link models. If the inflow to a link is varying over time, then to accurately model the link travel times or outflows varying over time would usually require modeling the flow, speed, and density evolving along the link. However, even when link inflows are varying over time, it has often been found convenient to express, o