Puget Sound Regional Council

In spring 2008, the SR 520 Tolling Implementation Committee was formed by the Washington State Legislature and charged with “…evaluating tolls as a means of financing a portion of the 520 Bridge Replacement and HOV Program…” To help the Committee complete its work, PSRC staff incorporated significant revisions and updates to its travel demand forecasting model so that it better emulated how people change their travel behavior in response to the implementation of tolling on a specific facility such as SR 520.

To help guide the model revision process, the Committee convened a peer review panel to evaluate and recommend improvements to the existing travel demand forecasting procedures. Specific improvements recommended by the panel and incorporated by PSRC staff included the use of consistent value-of-time assumptions across all model steps and the addition of vehicle operating costs to trip distribution impedance expressions. Following testing and validation, the updated model was provided to WSDOT staff who then 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.

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