Fleets are tracking two separate regulatory deadlines this month, one federal and one from California, that could each reshape near-term compliance planning for different reasons.
The U.S. Environmental Protection Agency’s public comment period on proposed changes to its Model Year 2027 heavy-duty NOx rule closes Saturday, August 29, 2026. The proposal would amend the 2023 rule under Docket ID EPA-HQ-OAR-2026-0728, and EPA held virtual public hearings on the proposal July 29 and July 30.
The changes under consideration would not alter the 2027 NOx emissions standard itself. Instead, they would roll back several compliance mechanisms EPA added in 2023. The proposal would rescind the extended emissions warranty, reverting from 10 years and 450,000 miles back to the current 5-year, 100,000-mile structure, and would delay the longer useful-life requirements until Model Year 2030. It would also eliminate the diesel exhaust fluid derate mechanism, which currently forces speed and power reductions when SCR systems are compromised, replacing it with visual and audible dashboard notifications instead. EPA estimates the warranty rollback alone could save up to $6,000 per diesel vehicle if manufacturers pass the savings to buyers.
Separately, the California Air Resources Board is working through its own deadline sequence tied to SB 253, the Climate Corporate Data Accountability Act. CARB released Modified Regulations for public comment on July 27, and that comment period closed August 11. The modifications would formally defer the first-year Scope 1 and Scope 2 greenhouse gas emissions reporting deadline from August 10 to November 10, 2026, for companies with more than $1 billion in annual revenue doing business in California. That November 10 date is not yet final. It remains contingent on the outcome of the comment period and subsequent approval by the state’s Office of Administrative Law.
CARB also confirmed that Scope 3 emissions reporting will not be required for the 2026 cycle, with a limited five-category Scope 3 phase-in proposed to begin in 2027. Large carriers, logistics companies, and other transportation-sector entities that meet the SB 253 revenue threshold have a dedicated stake in the outcome. CARB has scheduled a sector-specific listening session for energy, utilities, transportation, logistics, and waste management companies for August 26.
Both processes now move to agency review. EPA is expected to issue a final NOx rule sometime after August 29, likely before the end of 2026 given the rule affects Model Year 2027 equipment. CARB’s revised SB 253 regulation, once finalized, still requires Office of Administrative Law approval before the November 10 reporting deadline takes legal effect.
