The effects of realtime traffic information, supplied at the origin of the trip or along the way (en route), on the system's performance under alternative behavioural rules governing path selection in the network are examined in this paper. Simulation experiments are performed to investigate the effect on overall system performance as well as the incidence of benefits (costs) across user information groups of four experimental factors: (a) behavioural rules, governing users' response to realtime information, (b) sources of information, consisting of point-of-departure or in-vehicle (or both), (c) prevailing "initial conditions" in the system, and (d) market penetration (i.e., The fraction of users with access to realtime information in the network). The results of these simulation experiments provide insights into the effectiveness of realtime advanced driver information systems on systemwide performance and on its critical determinants. The results confirm a priori expectations that the existence of benefits as well as the relative effectiveness of origin-based versus en route information is highly dependent on the initial conditions prevailing in the system as well as the behavioural rules governing path selection. Extreme behaviour by users (with frequent switching in myopic response to any gain, no matter how small) could lead to severe worsening of traffic conditions under realtime information from either source. On the other hand, switching according to a boundedly rational model incorporating a threshold improvement in trip time is more likely to lead to meaningful systemwide benefits. This paper appears in Transportation Research Record No. 1306, In-vehicle Information Systems: modelling Traffic Networks and behavioural Considerations 1991.
Abstract