How truck emissions regulations work and what are the most important emissions rules today

The EPA’s latest major greenhouse gas regulation is “Final Rule: Heavy-Duty Vehicle Greenhouse Gas Emission Standards—Phase 3.” Adopted as a final rule in March 2024, the standard introduces stronger carbon dioxide emission standards for heavy-duty vehicles from model years 2027 through 2032 and beyond.

Emissions standards vary by equipment type and model year, ranging from 103.4 grams per ton-kilometer for model year 2027 Class 7 tractors with high roof to 45.4 g/tonne-kilometer for model year 2032 Class 8 tractors with day cab and high roof.

See also: Forget the carrot. EPA uses the stick.

What is CARB?

The EPA is not the only primary regulator of vehicle emissions. The California Air Resources Board sets emissions standards for California. Other states have the option to adopt CARB standards.

The Clean Air Act prohibits states from setting their own emissions standards—but with one key exception. The Clean Air Act allows states with existing emissions standards to apply for a waiver from setting their own emissions standards. California was the only state with existing emissions standards before the Clean Air Act, due to the state’s serious air quality problems.

Los Angeles established the nation’s first air pollution control program in 1947. In 1959, the state legislature established the California Motor Vehicle Pollution Control Board, which regulated vehicle emissions and later became the California Air Resources Board. The board set the nation’s first exhaust emission standards in 1966.

The federal government has consistently granted California emissions exemptions since the Clean Air Act was passed. In 2009, after the EPA recognized the public health threat posed by greenhouse gases, the agency granted California an exemption from regulating vehicle greenhouse gas emissions.

Other states have the option to adopt California’s emissions standards without requesting authorization. These states are sometimes called CARB states.

CARB regulations

Currently, the most important CARB regulations for heavy goods vehicles are:

• Heavy-Duty Omnibus, a standard that sets engine emissions standards for model year 2024–2027 equipment and restricts sales of older engines.
• Advanced Clean Trucks, which requires that the trucks OEMs sell include an increasing percentage of zero-emission vehicles over a period of several years.
• The Advanced Clean Fleets initiative requires fleets to transform their truck mix to increase the number of ZEVs over a period of several years.

CARB member states will not adopt all CARB regulations: CARB currently expects 10 states to adopt ACT, nine states to adopt Omnibus, and no states to adopt Advanced Clean Fleets.