Chapter 173-423 WAC
and Chapter 173-400 WAC

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.