Multistate Model for Travel Time Reliability

Travel time unreliability is an important characterization of transportation systems. The appropriate modeling and reporting of travel time reliability is crucial for individual travelers as well as management agencies. A novel multistate model is proposed for travel time modeling and reporting. The model advances travel time modeling in two aspects. First, the multistate model provides much improved model fitting as compared with single-mode models. Second and more important, the proposed model provides a connection between travel time distributions and the underlying travel time state. This connection allows for the quantitative evaluation of the probability of each travel time state as well as the uncertainty associated with each state, for example, the probability of encountering congestion at a given time of day and the expected travel time if congestion is experienced. A simulation study was conducted to demonstrate the performance of the model. The proposed model was applied to field data collected at San Antonio, Texas. The variation of the model parameters as a function of time of day was also investigated. The simulation study and field data analysis confirmed the superiority of the multistate model over the state-of-practice single-mode travel time reliability models and for ease of interpretation.