Chapter 173-423 WAC
and Chapter 173-400 WAC

Ecology is revising two rules. 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.

  • 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.

Rulemaking timeline


Announcement phase (CR-101)

Filing date:
Jan. 18, 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 others' 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.
   If you need help logging into the webinar, call 360-764-6663.

Rule proposal phase (CR-102)

Filing date:
Sept. 7, 2022

Rule proposal documents:

Comment period

Comments are due by October 19, 2022. We accept 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

Locationonline (webinar)
    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.