This page provides the Asphalt Binder Monthly Cost Index used for calculating asphalt cost price adjustments for contracts utilizing the Cost Price Adjustment GSP.

The Asphalt Binder Monthly Cost Index is established by WSDOT using the average of the current price of asphalt cement furnished by Poten and Partners, Inc. for the Pacific Northwest. The Western average is based on Poten and Partners, Inc's weekly averages for the Seattle, Washington area. The Eastern average is based on Poten and Partners, Inc's weekly averages for the Eastern Washington area including Northern Idaho. The Asphalt Binder Monthly Cost Index will be the average of the posted price from the last Friday of the current month to the last Friday of the previous month. If weekly price information ceases to be available from Poten and Partner's, Inc., WSDOT will select and begin using a substitute price sources or index to establish the asphalt monthly price averages at its discretion.

Projects in Northwest, Olympic and Southwest regions use the Western Index with the exception of Klickitat County which will use the Eastern Index.
Projects in North Central, Eastern and South Central use the Eastern average.

Asphalt Binder Monthly Cost Index: Eastern and Western Washington

The Western Index includes Clallam, Clark, Cowlitz, Grays Harbor, Island, Jefferson, King, Kitsap, Lewis, Mason, Pacific, Pierce, San Juan, Skagit, Skamania, Snohomish, Thurston, Wahkiakim, and Whatcom Counties.

The Eastern Index includes Adams, Asotin, Benton, Chelan, Columbia, Douglas, Ferry, Franklin, Garfield, Grant, Kittitas, Klickitat, Lincoln, Okanogan, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman and Yakima Counties.

*A project spanning Eastern and Western counties will use the index of the county that the majority of the work takes place in.

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