California Air Resources Board

In 2011, the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) jointly adopted the first federal GHG emission standards and fuel economy standards for heavy-duty engines and vehicles, referred to as the federal Heavy-Duty GHG Phase 1 regulation (Phase 1). That regulation requires both engine and vehicle manufacturers to employ more efficient components and systems. The federal Phase 1 standards took effect with model year (MY) 2014 tractors, vocational vehicles, and heavy-duty pick-up trucks and vans (PUVs) and the engines powering such vehicles. They did not set standards for trailers. 

In 2013, CARB approved for adoption California Phase 1 GHG regulations that were substantially identical to the federal Phase 1 regulations. This provided California the authority to certify new California certified engines and vehicles to the Phase 1 standards, as well as enforce them. Although the Phase 1 GHG standards will reduce emissions below the baseline of what they would be without any standards in place, they are not enough to offset the projected growth in heavy-duty truck vehicle miles traveled (VMT). From around 2023 forward, without standards stricter than Phase 1, GHG emissions from medium- and heavy-duty trucks would increase each year. A second phase of GHG standards, the Phase 2 GHG standards, are needed to offset that projected VMT growth and keep heavy-duty truck CO2 emissions declining. CARB staff worked closely with U.S. EPA and NHTSA over the past several years on the development of Phase 2 GHG standards. 

On October 25, 2016, U.S. EPA and NHTSA jointly adopted the federal Phase 2 standards that built on the Phase 1 standards and achieved additional GHG reductions. The federal Phase 2 standards follow the same regulatory structure as the federal Phase 1 standards. GHG emission standards are set for tractors, vocational vehicles, and PUVs. Separate engine standards are also established for the engines used in tractors and vocational vehicles. In addition, the federal Phase 2 standards establish for the first time, federal emissions requirements for trailers hauled by heavy-duty tractors. The federal Phase 2 standards are more technology-forcing than the federal Phase 1 standards, requiring manufacturers to improve existing technologies or develop new technologies to meet the standards. The progressively more stringent federal Phase 2 standards are phased-in from 2021 to 2027 for tractors, vocational vehicles, and PUVs. For trailers, the standards are phased-in from 2018 (2020 in California) through 2027.

In 2018, California aligned with the federal Phase 2 standards in structure, timing, and stringency, but with some minor California differences. This allowed manufacturers to continue building a single fleet of vehicles and engines for the U.S. market. In February 2019, the Office of Administrative Law (OAL) approved the rulemaking, and filed with Secretary of State.  The regulations are effective April 1, 2019. 

On June 29, 2021, the U.S. EPA amended the federal Phase 2 test procedures and other technical amendments to improve accuracy and reduce testing burden. As part of the Heavy-Duty Omnibus Regulation, CARB staff amended the California Phase 2 GHG regulation to clarify inadvertent ambiguities, correct some minor Phase 2 provisions, and aligned with certain provisions from U.S. EPA's technical amendments. The amendments were approved by OAL on December 22, 2021.