Transportation implementation plans

Ecology reviews how federal funding for transportation and highway projects and activities might impact air quality, to make sure they meet national air quality standards. Find out how we make sure transportation investments are consistent with air quality goals.

Making sure transportation funds support air quality

Transportation conformity is a process to make sure that federal transportation funds support highway and transit activities that are consistent with the State Implementation Plan (SIP) for air quality. The federal Clean Air Act requires transportation conformity in certain areas, including:

In these areas, air quality and transportation planners are required to review transportation plans and projects before they are approved or funded to make sure they do not:

  • Result in new air quality violations.
  • Make air quality violations more frequent or severe.
  • Delay compliance with federal air quality standards.

Enforceable limits on air pollution from transportation sources

Attainment and maintenance state implementation plans must include enforceable limits on the total amount of air pollution from vehicles and other transportation sources. These limits are called “motor vehicle emissions budgets” or MVEBs. They are a ceiling of total emissions that cannot be exceeded.

Regional review of transportation conformity plans

Regional transportation planners evaluate if future emissions from transportation sources will meet (conform to) the limits included in the plan. This is called a transportation conformity determination.

The Metropolitan Planning Organization (MPO) or Regional Transportation Planning Organization (RTPO) located in the area makes transportation conformity determinations for:

  • Long-range transportation plans.
  • Transportation improvement programs.
  • Projects funded by the Federal Highway Administration and the Federal Transit Administration.

If future emissions from transportation sources are below the limits in the plan, the region can start implementing the plan or project. If emissions exceed the limits, then the region must make changes or implement additional measures to reduce air pollution before they can start again.

Interagency consultation

We consult with several agencies in the transportation conformity process, including: