Four regulatory programs shape the zero-emission and low-emission future of Class 5–8 trucks in the United States. The California Air Resources Board's Advanced Clean Trucks (ACT) rule requires manufacturers to sell rising percentages of ZEV heavy-duty vehicles, adopted by roughly a dozen Section 177 states. CARB's Advanced Clean Fleets (ACF) rule targets fleet operators with ZEV purchase and drayage deadlines, but enforcement is paused after California withdrew its EPA waiver request in January 2025. The federal EPA 2027 Heavy-Duty Low-NOx rule cuts allowable NOx emissions roughly 80% for model year 2027 engines nationwide. And California's Heavy-Duty Omnibus rule imposes tighter NOx limits and longer warranty requirements on engines sold in California starting with MY2024. This tracker lists 16 milestone events across these programs, categorized by status. Fleet planners and truck dealers — especially those operating on the West Coast — use this page as a reference for compliance timelines.
| Date | Jurisdiction | Program | Status | Milestone | Source |
|---|---|---|---|---|---|
| 2026-03-18 | Multi-state | Advanced Clean Trucks (ACT) | pending | DC Circuit hears ACT waiver challenge Oral arguments begin in the DC Circuit on the legality of the Congressional Review Act resolution rescinding the ACT waiver. Decision expected late 2026. | Source → |
| 2026-01-01 | California | CARB Heavy-Duty Omnibus | in-effect | CARB Omnibus Phase 2 limits apply to MY2026 engines Phase 2 Omnibus NOx limits apply to MY2026 heavy-duty engines sold in California, with tightened in-use testing thresholds and extended emissions warranty. | Source → |
| 2025-09-30 | Federal | EPA 2027 Heavy-Duty Low-NOx | scheduled | EPA confirms 2027 NOx rule compliance timeline EPA reiterates that the 2027 heavy-duty NOx rule remains in force for MY2027 engines nationwide and publishes certification guidance for engine OEMs. | Source → |
| 2025-06-12 | Multi-state | Advanced Clean Trucks (ACT) | pending | Section 177 states evaluate ACT path forward Oregon, Washington, New York, New Jersey, Massachusetts, Vermont, Colorado, and Maryland review whether ACT obligations remain enforceable after the federal waiver revocation; litigation filed in the DC Circuit. | Source → |
| 2025-05-22 | Federal | Advanced Clean Trucks (ACT) | blocked | Congress revokes California ACT waiver Congress passes a Congressional Review Act resolution revoking the EPA waiver that authorized California's ACT rule, with downstream effect on Section 177 states that adopted ACT. | Source → |
| 2025-02-14 | California | CARB Advanced Clean Fleets (ACF) | blocked | California enforcement of ACF suspended CARB confirms it will not enforce ACF purchase mandates against fleets pending a future waiver path. Voluntary HVIP incentives and port-specific ZEV mandates remain. | Source → |
| 2025-01-13 | California | CARB Advanced Clean Fleets (ACF) | blocked | CARB withdraws ACF waiver request Days before the Biden EPA was expected to decide, CARB withdraws its ACF Clean Air Act waiver request, effectively pausing enforcement of the drayage and high-priority fleet ZEV purchase mandates. | Source → |
| 2024-06-30 | Multi-state | Advanced Clean Trucks (ACT) | in-effect | Massachusetts, New York, Vermont enforce ACT for MY2025 Massachusetts, New York, and Vermont begin enforcing ACT manufacturer quotas with the MY2025 model year. Colorado and Maryland are phased in for MY2027. | Source → |
| 2024-04-25 | Federal | EPA Phase 3 Greenhouse Gas | scheduled | EPA finalizes Phase 3 heavy-duty GHG rule EPA issues final Phase 3 GHG standards for MY2027-2032 heavy-duty vehicles, tightening CO2 targets alongside the 2027 NOx rule. | Source → |
| 2024-01-01 | California | CARB Heavy-Duty Omnibus | in-effect | CARB Heavy-Duty Omnibus Low-NOx takes effect for MY2024 CARB's Heavy-Duty Omnibus rule begins applying to MY2024 engines sold in California, cutting NOx limits ~75% and extending warranty and useful-life requirements. | Source → |
| 2023-12-28 | California | CARB Advanced Clean Fleets (ACF) | pending | CARB submits ACF waiver request to EPA California formally requests the Clean Air Act preemption waiver needed to enforce ACF against drayage and high-priority fleets. | Source → |
| 2023-08-15 | New Jersey | Advanced Clean Trucks (ACT) | in-effect | New Jersey finalizes ACT adoption New Jersey DEP adopts ACT, requiring manufacturers to meet ZEV sales percentages beginning MY2025 for Class 2b-8 vehicles sold in state. | Source → |
| 2023-04-28 | California | CARB Advanced Clean Fleets (ACF) | pending | CARB adopts Advanced Clean Fleets rule ACF requires high-priority and federal fleets to begin ZEV purchases in 2024 and mandates a 100% ZEV drayage fleet at California ports by 2035. Rule is contingent on an EPA preemption waiver. | Source → |
| 2022-12-20 | Federal | EPA 2027 Heavy-Duty Low-NOx | scheduled | EPA finalizes 2027 heavy-duty NOx rule EPA issues the Heavy-Duty 2027 final rule cutting allowable NOx emissions ~80% from current limits, with new on-board diagnostics and a 435,000-mile useful-life standard. | Source → |
| 2021-12-08 | Multi-state | Advanced Clean Trucks (ACT) | in-effect | Oregon and Washington adopt ACT Oregon and Washington finalize ACT adoption, aligning manufacturer ZEV sales quotas with California beginning MY2025. | Source → |
| 2020-06-25 | California | Advanced Clean Trucks (ACT) | in-effect | CARB adopts Advanced Clean Trucks rule The California Air Resources Board adopts ACT, requiring manufacturers to sell rising percentages of zero-emission Class 2b-8 trucks starting with model year 2024. | Source → |
Advanced Clean Trucks is a California Air Resources Board rule adopted in 2020 that requires manufacturers to sell a rising percentage of zero-emission Class 2b-8 vehicles in California each year. Roughly a dozen other states including Oregon, Washington, New York, New Jersey, Massachusetts, Vermont, Colorado, and Maryland adopted ACT under Clean Air Act Section 177. A 2025 Congressional Review Act resolution revoked the federal waiver supporting ACT and its downstream enforcement in Section 177 states is now being litigated.
Advanced Clean Fleets is a separate CARB rule adopted in April 2023. Unlike ACT, which targets manufacturers, ACF targets fleet operators. It requires high-priority fleets and federal fleets to begin ZEV purchases in 2024 and calls for a 100% ZEV drayage fleet at California ports by 2035. ACF requires a Clean Air Act preemption waiver from EPA, which California withdrew in January 2025, effectively pausing enforcement.
Yes. The EPA 2027 heavy-duty low-NOx rule was finalized in December 2022 and applies nationwide for model year 2027 heavy-duty engines. It cuts allowable NOx emissions by roughly 80% from current limits, extends the useful-life requirement to 435,000 miles for most categories, and tightens on-board diagnostics. Unlike ACT and ACF, it is a federal rule and does not require a California waiver.
The Heavy-Duty Omnibus is a California-specific low-NOx rule that took effect in phases starting with MY2024 engines. It imposes tighter NOx limits than the federal rule, longer warranty and useful-life requirements, and in-use testing obligations. Engines sold in California must be certified to Omnibus standards; engines sold outside California generally follow the EPA 2027 standard on the federal timeline.
They are separate rules with separate waiver paths. The 2025 Congressional Review Act resolution targeted the ACT waiver specifically. ACF never had an active waiver — California withdrew its ACF waiver request in January 2025 before EPA could decide. The practical effect is that neither ACT nor ACF is currently being enforced, although Section 177 states and CARB are pursuing litigation and future waiver strategies.
West Coast fleets and port drayage operators should still plan around the ACF 2035 drayage goal and local port-specific ZEV mandates, both of which remain in force independent of the ACF waiver. All fleets nationwide need to plan around the federal EPA 2027 NOx rule, which is not contingent on California. Dealers selling into California should track Omnibus certification status of each engine family because MY2026-2027 availability differs between California-legal and 49-state configurations.