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 county-wide in 1990. The TDT went into effect on 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).

The 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.

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

January 2015 Project List Amendments

Ten jurisdictions proposed amendments to the TDT Capital Improvements Project List (Appendix C) to be consistent with recent transportation system plan updates and to respond to other changing conditions. The Washington County Coordinating Committee (WCCC) approved the amendments on January 5 and forwarded them to the Board of County Commissioners, which adopted them on January 20. Changes to the list are documented and described in the links below. The amended lists (both road and transit project lists) are provided as Appendix C listed under the TDT Code Language & Rules in the right column of this webpage.

Proposed Amendments to TDT Road Project List

Proposed Amendments to TDT Transit Project List

Memo to WCCC (January 5, 2015)

TDT Rates Increase - Effective July 1, 2017

At its April 25, 2017 meeting, the Board of Commissioners adopted an increase to the TDT rates by 2.174% effective July 1, 2017. 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.

TDT Rates Increase - Effective July 1, 2016

At its April 19, 2016 meeting, the Board of Commissioners adopted an increase to the TDT rates by 2.028% effective July 1, 2016. The rate adjustment is based upon the TDT index; an index reflecting a five-year rolling average in the cost of road construction, labor and right-of-way.

TDT rates beginning July 1, 2015

At its April 21, 2015 meeting, the Board of Commissioners adopted to increase TDT rates by 0.962% effective, July 1, 2015. This is the first TDT rate increase caused by the TDT index; an index based upon percentage changes in the cost of road construction, labor and right-of-way, using a five-year running average.

October 1, 2014 Rate Changes

On August 5, 2014 the Board of County Commissioners adopted an ordinance modifying the TDT, A-Engrossed Ordinance 793. The ordinance implements Board direction given in March 2014 to:

  • End the TDT rate discounts that have been in effect since 2009;
  • Lock in TDT rates at the time of building permit acquisition, even if deferring payment until occupancy;
  • Make the Change-in-Use Discount permanent for small commercial spaces.

Ordinance 793 Timeline

  • July 3, 2014 - County Counsel files Ordinance 793
  • July 15, 2014 - First reading of the ordinance 
  • August 5, 2014 - Second reading and first public hearing; ordinance adopted.
  • October 1, 2014 - Changes become effective

Ordinance 793 - Cover, Exhibit & Appendices format-pdf

Ordinance 793 Staff Report 8-5-14

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%. At the request of the Washington County Coordinating Committee, the Board of County 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% for buildings three years or older, and 75% for buildings 20 years or older. The discount was made permanent through A-Engrossed Ordinance 793, adopted on August 5, 2014.