Traffic equilibrium and system reliability in stochastic transportation networks.

摘要

This research provides a framework of analyzing the stochastic transportation networks with consideration of random link travel time, traffic demand and roadway capacity. The study focuses on the problem of predicting traffic flows under traffic equilibrium within the framework of decision-making in a probabilistic transportation network, and follows up with the system reliability analysis under stochastic network conditions.;In the risk-based traffic equilibrium problem, the randomness of the underlying transportation network is incorporated into the traditional traffic equilibrium models by differentiating travelers' risk-taking behaviors with respect to probabilistic travel times. The travel time risk is quantified directly from the probability distribution of travel time random variables, and is embedded in the route choice conditions. The classification of different risk-taking behaviors is based on travelers' preferred travel time risks. The formulation of the risk-based traffic equilibrium model clarifies that travelers with different risk preferences have the same objective to save travel time cost, though they may make different route choices. The model is first formulated with fixed traffic demand. Then it is generalized to incorporate the effect of demand variation. The proposed solution algorithm is applicable for networks with Normal distributed link travel times theoretically. Further simulation analysis shows that it can also be applied to approximate the equilibrium network flows for other frequently used travel time distribution families of Gamma, Weibull and Log-Normal.;The study aims to provide a systematic approach of analyzing various random factors in a stochastic transportation network. To measure the effect of various environmental variables on the network performance, the system reliability is examined with possible capacity variation. The objective is to present an overall performance measure of the transportation network regarding whether the network is reliable to accommodate the traffic demand.;A medium size transportation network is used to demonstrate the application of the proposed risk-based traffic equilibrium model and the reliability analysis method. The results show that the model captures travelers' risk-taking behaviors more realistically and flexibly compared with existing stochastic traffic equilibrium models. The reliability analysis provides information about capacity adequacy and guidelines for network improvements.