Chapters 173-423 and 173-400 WAC – Clean Vehicles Program

On December 19, 2022, Ecology adopted two rules. Ecology is directed by the Motor Vehicle Emission Standards law (RCW 70A.30.010) to adopt California vehicle emission standards, including the zero-emission vehicle (ZEV) program, and maintain consistency with California’s standards and Section 177 of the federal Clean Air Act.

  • Chapter 173-423 WAC, Clean Vehicles Program
    • ​Adopts California's rules:
      • Heavy-Duty Engine and Vehicle Omnibus rules and associated amendments – Starting in model year 2026, these rules require that new internal combustion engines for heavy-duty vehicles emit much lower quantities of nitrogen oxides (NOx), particulate matter (PM), and greenhouse gases.
      • Advanced Clean Cars II – This rule will increase the percentage of passenger cars, light duty trucks, and medium duty vehicles solid in Washington that are zero-emission vehicles (ZEVs). The sales mandate would take effect in model year 2026 and begin by requiring 35% of new passenger vehicles sales to be zero-emission vehicles. That percent will increase 6-9% per year until zero-emission vehicles make up 100% of new sales starting in model year 2035. It will also require light and medium duty vehicles to meet stronger emission standards.
    • Includes the following provisions to support Ecology's implementation of California's emission standards:
      • Early action zero-emission vehicle credits – This rule provides automakers with optional zero-emission sales credits for model years 2023 and 2024. This would:
        • Incentivize increased zero-emission vehicle sales.
        • Make sure Washingtonians have access to a wide variety of zero-emission vehicle models before the regulatory requirements take effect in model year 2025.
        • Allow participating automakers to bank credits to meet future compliance requirements under ACC I and II.
      • One-time fleet reporting – This requires owners and operators (such as businesses, government agencies, municipalities, brokers, freight dispatchers, transit agencies, etc.) to report information about medium- and heavy-duty vehicles (defined as vehicles over 8,500 pounds) in their fleets by September 30, 2023. This requirement mirrors a similar requirement in California’s Advanced Clean Trucks rule. Ecology currently has very little data on fleets. The inventory of existing heavy-duty fleets and information about where the vehicles operate will help Ecology develop and implement strategies to reduce their emissions.​
  • Chapter 173-400 WAC, General Regulations for Air Pollution Sources
    • Updates the adoption date of federal rules. Ecology can only implement and enforce federal rules that the rule adopts by reference. This rule amends 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.

Rulemaking timeline


Announcement phase (CR-101)

Filing date:
Jan. 17, 2022

Announcement documents

Rule development phase

January 18, 2022 – September 6, 2022

Public input & involvement

Public comment period (informal) – EXTENDED
February 21, 2022 – June 21, 2022 (originally May 29, 2022)

Read comments.

Ecology's meetings with stakeholders

Date Documents Location
February 28, 2022
9 a.m. – 11 a.m.
ZEV credit options

webinar 1

April 19, 2022
9 a.m. – 11 a.m.
Draft rule language
ZEV credit options

webinar 1

June 14, 2022
9 a.m. – 11 a.m.
Draft rule language
webinar 1

1 Webinar information:
   Register for each webinar to get your meeting ID and passcode.
   To hear the webinar better or to call in only, use your phone (instead of the computer) to call 253-215-8782.

Rule proposal phase (CR-102)

Filing date:
Sept. 6, 2022

Rule proposal documents:

Comment period

Comments were due by October 19, 2022. We accepted comments in the following ways:

  • Attend a public hearing online (webinar):
    October 12, 2022 at 1 p.m.
  • Mail to:  Adam Saul
       Department of Ecology
       Air Quality Program
       P.O. Box 47600
       Olympia, WA  98504-7600

Public hearing

Date/time:  October 12, 2022 at 1 p.m. online webinar

Location:  online (webinar) – recording
    Register for the webinar to get your access code and password.
    To hear the webinar better or to call in only, use your phone (instead of the computer) to call 253-215-8782.

Agenda: Presentation, question-and-answer session, followed by public hearing

Accessibility:  To request ADA accommodation for the public hearing, email Ecology’s ADA coordinator by October 7, 2022.  Or call (360) 407-6831, 711 (relay service), or 877-833-6341 (TTY).

Additional languages

Español (Spanish) 中文 (Chinese) Tiếng Việt (Vietnamese) 한국어 (Korean)


To request ADA accommodation for disabilities, or printed materials in a format for the visually impaired, contact Ecology's ADA Coordinator by email at, or call 360-407-6831. People with impaired hearing may call Washington Relay Service at 711. People with speech disability may call TTY at 877-833-6341.