Puget Sound Regional Council

In spring 2008, the Washington State Legislature formed the SR 520 Tolling Implementation Committee. The committee was charged with evaluating tolls as a means of financing a portion of the 520 Bridge Replacement and HOV Program.

To help the committee, PSRC staff incorporated significant revisions and updates to the travel demand forecasting model. These changes helped better emulate how people change their travel behavior in response to tolling on a specific facility such as SR 520.

Peer Review Panel Guidance

The committee convened a peer review panel to help guide the model revision process. This panel evaluated and recommended improvements to existing travel demand forecasting procedures. Improvements recommended by the panel and incorporated by PSRC staff included using consistent value-of-time assumptions across all model steps and adding vehicle operating costs to trip distribution impedance expressions.

WSDOT Model Runs

Following testing and validation, the updated model was provided to WSDOT staff. They conducted numerous 2010 and 2020 model runs to provide estimates of corridor travel demand and diversion for each of ten tolling scenarios on SR 520 or on both SR 520 and I-90.

Study Completion

The modeling work was completed during fall 2008 and the Final Report of the SR 520 Tolling Implementation Committee was submitted to Washington State Legislature in January 2009.

Puget Sound Regional Council • 1011 Western Ave, Suite 500 • Seattle, WA 98104 • 206-464-7090