Using a DTA model to evaluate road tolling strategies: Seattle Experience

Recent applications and research in toll modeling suggest that Dynamic Traffic Assignment (DTA) modeling is gaining acceptance in the industry as a suitable modeling platform for a variety of planning studies and projects. DTA models differ from traditional static travel demand models in that they explicitly consider travel flow dynamics, i.e., modeled conditions are time-dependent. Within this context are varying levels of DTA models ranging from more general macroscopic applications for regional networks to detailed microscopic simulation-based models used for smaller subarea analyses. In between these extremes are mesoscopic simulation-based DTA models. By blending the traffic assignment capabilities of travel demand modeling tools with the intersection/link operational analysis characteristics of traffic simulation tools, mesoscopic DTA modeling effectively bridges the “gap” between the more commonly used macroscopic and microscopic paradigms. This paper summarizes a current effort to utilize a simulation-based DTA model—which incorporates multiple user classes—to support updates to the tolling and revenue analysis for the Alaskan Way Viaduct Replacement Tunnel Project in Seattle, Washington. The primary objective of this effort is to efficiently and accurately test and assess the effects of tolls on both revenue generation and traffic network operations. The reasons for choosing DTA to meet this objective are described and along with an overview of the study methodology and tolling model development process. Results, findings and lessons learned from the study are summarized. Potential future applications of the model are discussed, along with how this work can add value to toll modeling/forecasting.