Chapter 173-423 WAC
and Chapter 173-400 WAC

Ecology proposes to update two rules:

This rulemaking will:

  • Adopt California's Heavy-Duty Engine and Vehicle Omnibus Regulation and associated amendments. These rules require cleaner, less polluting heavy-duty engines.
  • Adopt California’s Advanced Clean Cars II. This rule will increase zero emission vehicle (ZEV) sales of passenger cars, light-duty trucks, and medium-duty vehicles to 100 percent starting in 2035.
  • Update the adoption date of California’s rules.

This rulemaking will include:

  • Advanced Clean Cars II – evaluate and potentially adopt credit options
  • Credit for ZEV sales – evaluate and potentially adopt provisions to provide a manufacturer with credits for a ZEV sale before our program starts in 2024
  • Fleet reporting – require fleet owners, businesses, government agencies, municipalities, brokers, transit agencies, etc. to report information about vehicles over 8,500 pounds

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 the state. 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 are also updating five sections of Chapter 173-400 WAC:  Sections -025, -050, -070, -115, -720. In Section -720, the rule will keep the current definition of “project emissions accounting.

Rulemaking timeline


Announcement phase (CR-101)

Filing date:
Jan. 18, 2022

Announcement documents

Rule development phase

January 18, 2022 – Summer 2022

Public input & involvement

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

Comment online and 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.
coming soon 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.

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.