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Comment Period

Clean Vehicles Program, Chapter 173-423 WAC

Proposed rulemaking

Sept. 7, 2022 - Oct. 19, 2022, 11:59 p.m.

Ecology is revising two rules: Chapter 173-423 WAC, Clean Vehicles Program and Chapter 173-400 WAC, General Regulations for Air Pollution Sources.

Ecology is directed by the Motor Vehicle Emission Standards law (RCW 70A.30.010) to adopt California vehicle emission standards and maintain consistency with new versions of California’s rules. This rulemaking will update:

  • Chapter 173-423 WAC, Clean Vehicles Program
    • ​Adopt California's Advanced Clean Cars II rule which will ramp up sales of zero emission vehicles (ZEVs) in Washington, starting in model year 2026.
    • Adopt California's Heavy-Duty Engine and Vehicle Omnibus rules, which require cleaner, less-polluting heavy-duty engines.
    • Establish a credit system for ZEV sales in model years 2023 and 2024, before regulatory requirements take effect.
    • Establish a one-time fleet reporting requirement for owners and operators of large vehicle fleets.
  • Chapter 173-400 WAC, General Regulations for Air Pollution Sources
    • Update adoption date of federal rules by amending sections:
      • WAC 173-400-025 – Adoption by reference
      • WAC 173-400-050 – Emission standards for combustion and incineration units
      • WAC 173-400-070 – Emission standards for certain source categories
      • WAC 173-400-115 – Standards of performance for new sources
      • WAC 173-400-720 – Prevention of significant deterioration (PSD). The rule will keep the current definition of "project emissions accounting."

Motor vehicles are the largest source of air pollution in Washington. Transportation contributes about 22 percent of total air pollution and 45 percent of greenhouse gas emissions throughout Washington. Along with cutting greenhouse gases, reducing vehicle emissions will improve air quality and protect public health, especially for people living near a highway or road with a lot of traffic.


We write rules to implement and enforce state and federal environmental laws and rules.  Ecology follows a three-phase process for rulemaking:

  1. Announcement and development
  2. Proposal
  3. Adoption

For each phase of the process, we update the rulemaking web page and notify interested parties. We also file notice in the Washington State Register. To learn more about Ecology’s rulemaking process, read the Frequently Asked Questions.

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Adam Saul
Washington Department of Ecology
Air Quality Program
P.O. Box 47600
Olympia, WA 98504-7600
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Adam Saul
Rulemaking Lead
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