Introduction

Abstract

Dynamic traffic routing (DTR) refers to the process of diverting traffic at a junction dynamically. Static diversion would be the case when the amount of traffic to be diverted has been pre-calculated and does not change with time. Being dynamic implies that the values change with time as the traffic conditions also change. Figure 1.1 shows a sample site where dynamic traffic routing would be highly beneficial. This is a traffic site where most of the traffic travels from point A to point B in the morning rush hours and in the reverse direction during the evening hours. There are two highways, which are connected at point A. Vehicles that want to go to point B can take either of the two highways, and normally they take a comparable amount of time. If there is congestion in one of the routes, then the travel time on that route will increase. Hence, more traffic should be diverted onto the other route. In general, if the travel time is the same on both routes, we can claim that this traffic system is working well. Therefore, when we develop traffic controllers in this book, we will keep equal travel time as one of the objectives of the control. This objective is called “user equilibrium” since users try to or would like to emulate that kind of route choice behavior to obtain maximum benefit. Another objective would be to obtain “system optimal,” which means that for the total traffic network, the overall time created by using the specific choice of traffic diversions at all traffic nodes is optimal (implying that it is less than the total travel time created by any other choice of diversion strategy).