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Environment - Air Quality

What does WSDOT do to improve air quality?

For more info on air quality, read our Air Quality Folio (pdf 688 kb) and additional air quality resources.

Information on how we address climate change in project documents is on our Energy page.  Additional information on what WSDOT is doing about climate change in on our main climate change page.

How does WSDOT analyze air quality?

WSDOT requirements for air quality analysis are described in Chapter 425 of the WSDOT Environmental Procedures Manual (EPM). 

The Air Quality Checklist (pdf 12 kb) outlines documentation requirements used for WSDOT review and approval and can be used to help with project scoping.
If you are working on a WSDOT project and need an air quality analysis, please submit a completed Task Request Form (doc 167 kb) to Jim Laughlin.

WASIST cannot be used for analysis that begins after December 20, 2012.  WASIST: WSDOT’s carbon monoxide (CO) intersection screening tool, is based on air quality models that have been replaced.  WASIST can still be used for CO analysis that began before December 20, 2012.  All new air quality modeling must be based on EPA MOVES and either AERMOD or CAL3QHC/-R models. 

WSDOT is working with FHWA on streamling tools for CO and will update this site when those tools are available.

Regulatory Compliance

The Clean Air Act (CAA) requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS)for six common air pollutants, also known as "criteria pollutants.

Transportation conformity applies to projects funded by the Federal Highway Administration (FHWA) and the Federal Transit Administration (FTA).  Conformity requirements apply to areas that do not meet ("nonattainment area"), or previously did not meet ("maintenance area"), the NAAQS. 

When an area violates the standard for one of these pollutants, a State Implementation Plan (SIP) is developed to outline the strategies for attaining the standard.  When conformity applies to an area, transportation projects must demonstrate conformity to the SIP at the regional and project levels.

Regional Conformity
-  Emissions from regionally significant transportation projects within, and contributing to, the nonattainment/maintenance area must be within the allowable emissions limits, or "motor vehicle emissions budget" (MVEB)," for transportation.

Regional conformity is demonstrated by the regional planning organization(s).  In Washington State, regional planning organizations, such as the Puget Sound Regional Council, coordinate local transportation projects in transportation implementation plans every four years. These individual plans are complied into multi-sector plans by the local clean air agencies. In the Puget Sound region, the Puget Sound Clean Air Agency has this responsibility. These plans must show that the projects conform with state and federal regulations. 

If a transportation plan can't demonstrate conformity, federal funding from FHWA and FTA can be restricted for some projects in the nonattainment/maintenance area.

Project Level Conformity - Projects within a nonattainment/ maintenance area that have the potential to increase emissions for the pollutant of concern are subject to project level conformity.  For example, adding a traffic signal to a CO maintenance area has the potential to increase idling and, therefore, CO emissions.

Where project level conformity applies, the project sponsor, e.g., WSDOT, must models emissions to determine project level conformity.

The Federal Highway Administration's (FHWA) Air Quality site provides more information about the air quality requirements for transportation projects. Before a project is built, we must show that it will not adversely affect air quality. The FHWA Conformity site describes regulations governing these analysis. 

What pollutants does WSDOT evaluate?

WSDOT evaluates each project for its effects on our air quality according to the Air Quality Chapter of the WSDOT Environmental Procedures Manual. We focus on four primary types of pollutants:

  • Carbon Monoxide - significant quantities, can inhibit the body's ability to take up oxygen. However, carbon monoxide is no longer much of a problem because of improved vehicle exhaust systems. Nonetheless, conformity regulations require us to analyze carbon monoxide concentrations at project intersections.
  • Particulate matter - (e.g., dust, smoke, and diesel exhaust) also negatively affects human health, especially the respiratory system. Particulate matter is produced both as a byproduct of combustion and from dust released into the air. Regulations regarding particulate matter are changing to require tighter controls on these emissions.
  • Mobile source air toxics (MSATs) are a group of chemicals prioritized by the EPA for reduction in transportation projects. These chemicals are known to adversely impact human health. See our WSDOT Summary of MSAT Analysis in NEPA/SEPA Documents (pdf 73 kb) for more information.

What is WSDOT working on with others?

WSDOT has collaborated with a number of public, private, and non-profit partners to reduce vehicle air pollution. 

  • The Puget Sound Maritime Air Forum is working to reduce air pollution at ports in the Northwest.
  • Cascadia Center supports the development of a balanced, integrated, and expanded transportation system for people and goods in Washington, Oregon, and British Columbia. This center is part of the Discovery Institute.
  • The annual Faster Freight - Cleaner Air conference covers resources and solutions to reduce emissions while improving operations.

What is WSDOT doing to reduce its own emissions?

Within the agency we are working to reduce our emissions as well. Some of the steps we have taken include

  • Reducing idle times. Our no-idle policy (pdf 362 kb) instructs employees to turn off engines when they are not needed to reduce idling. This both reduces air pollutants and saves fuel. In addition to reducing idling in vehicles, we are also implementing this easy strategy for equipment that is not being used.
  • Mowing less often. Our maintenance crews are mowing the right of way area next to the roads less frequently. Again, while reducing air pollutants, this also conserves fuel.
  • Installing LED lights. We are installing LED warning lights on many vehicles. With these high-efficiency lights we can turn the engine off without worrying about running down the batteries. Many traffic signals have also been replaced with LED lights.

What is being done to reduce diesel pollution?


In addition, to further address diesel exhaust, in 2002 the EPA released new standards for diesel fuel reducing the allowable sulphur levels.

Additional air quality resources