On-line traffic assignment and network loading

Consider the following scenario, which is very applicable, for example, to cities like Tucson, Arizona, that have several sections within a ‘work zone’ to upgrade network infrastructure.Work zones invariably lead to changes in traffic patterns providing a challenge to traffic management and planning departments to minimize the disruption caused to motorists. This is especially so in the immediate neighborhood of the work zone, although it is conceivable that a work zone at a critical location can impact a large segment of the network. In particular, one needs to estimate the re-routing and resulting traffic loading for this purpose. Similar concerns are also raised by major traffic incidents whose impacts last for several days, local flooding and, in general, when a portion of network infrastructure is damaged to the point where some motorists avoid it. In order to forecast the network load, several issues arise: (i) Which routes will carry the displaced loads? (ii) Will there be some sort of traffic equilibrium among the routes? (iii) If so, how long will it take to reach this equilibrium? (iv) What is the role of traffic measurements, such as detector data and travel times from probe vehicles? These are some of the issues addressed in this chapter.