Transportation Development Tax / TDT


Transportation Development Tax 
Tax on new development, dedicated to transportation improvements.

On Tuesday, Nov. 4, 2008, the citizens of Washington County approved Measure No. 34-164, the Transportation Development Tax (TDT). The TDT replaced the previous tax, known as the Traffic Impact Fee (TIF), passed countywide in 1990. The TDT went into effect July 1, 2009, increasing the previous TIF rates as well as updating and clarifying various procedures. Now fully phased-in, the TDT has essentially doubled the rates developers pay for the impact new development has on the transportation system. The TDT is levied countywide including within the cities.

The TDT has been thoroughly reviewed by the Washington County Coordinating Committee (WCCC). The TDT is based on the estimated traffic generated by each type of development. All revenue is dedicated to transportation capital improvements designed to accommodate growth. Eligible projects are on major roads, including sidewalks and bike lanes, as well as transit capital projects (such as bus shelters).

TDT is not a property tax. The TDT is imposed on all new development in Washington County, except for temporary uses that will exist for no more than 90 days, and remodeling or replacement of existing  uses, except to the extent that remodel or replacement of a use increases its capacity to intensify demands on the transportation system.
The TDT is collected prior to the issuance of a building permit; or in cases where no building permit is require(such as for golf courses or parks), prior to final approval of a development application. Options exist, however, for payment of the tax over time, or in certain cases, deferral of payment until occupancyCredit toward the TDT may also be approved for constructing eligible transportation improvements.

TDT rates were scheduled to be phased over a 4-year time period. Because of the recession, the Board of Commissioners adopted a series of ordinances which delayed the final step-increase of the TDT rate phase-in schedule until October 1, 2014. 

TDT Rates Increase - Effective July 1, 2019

At its April 16, 2019 meeting, the Board of Commissioners adopted an increase to the TDT rates by 3.005% effective July 1, 2019. The rate adjustment is based upon the TDT index, reflecting a five-year rolling average in the cost of road construction, labor and right-of-way.

For more information, please contact Long Range Planning at 503-846-3519 or e-mail

Discount for Change of Use

Applicants changing the use of an existing building may be eligible for a TDT discount as high as 75 percent. At the request of the Washington County Coordinating Committee, the Board of Commissioners considered and approved a temporary discount under Ordinance 751. Discount eligibility is limited to buildings at least three years old that are changing to certain commercial, industrial or office uses. Discounts are applied to the first 5,000 square feet of floor area, and are calculated at 50 percent for buildings three years or older, and 75 percent for buildings 20 years or older. The discount was made permanent through A-Engrossed Ordinance 793, adopted Aug. 5, 2014.


TDT Forms 

TDT Code Language & Rules


Manuals and Reports


TDT Election Materials


Adopted Ordinances