Route choice and advanced traveler information systems on a capacitated and dynamic network

Much of the push behind Intelligent Transportation Systems (ITS) has come from the hope that providing travelers with better information will result in reduced travel time and traffic congestion. Phase 1 of the United States’ IVHS National System Architecture project, for instance, made ATIS (Advanced Traveler Information Systems) the centerpiece of its benefits evaluation, and ATIS has been the subject of numerous traffic simulation studies. The objective of this paper is to examine the ‘informational’ assumptions embedded in traffic simulations, and to assess how these assumptions affect simulation results. Most importantly, this paper examines the hypothesis that increasing market penetration can lead to a decrement in network performance. The paper proves, for a simple parallel network, that increasing the market penetration of accurate information cannot harm network performance. For this same network, the paper shows that increasing the penetration of instantaneous travel time estimates might degrade network performance. The paper also asserts that the existance, or non-existence, of an optimal market penetration is moot. The suggestion is that ATIS should not be viewed as a strategy for achieving system optimal traffic distributions. ATIS should instead be viewed first as a service to the public, to improve their confidence and comfort in using the system, and second as a means for steering traffic away from dis-equilibrium behavior and toward user optima that utilize alternate routes where feasible.