If you’ve ever tried to plan a family road trip while your GPS keeps yelling “recalculating,” congratulationsyou
already understand the mood of the U.S. heavy-duty truck market right now. The regulatory route is changing mid-drive,
and everyone from engine engineers to fleet managers is gripping the steering wheel a little tighter.

In 2025, Congress used the Congressional Review Act (CRA) to wipe out key Clean Air Act waiver decisions
that had allowed California to enforce some of the nation’s toughest heavy-duty emissions programs. The President signed
the CRA disapproval resolutions in June 2025, and the result has been a classic case of regulatory whiplash:
manufacturers and fleets are still expected to make billion-dollar decisions (and multi-year product plans) while the legal
and policy ground under them is shifting.

This article breaks down what the CRA action did, which heavy-duty rules are caught in the crosswinds, and what “in flux”
really means for trucks, buses, vocational vehicles, and the businesses that depend on them. (Spoiler: it means spreadsheets
with more tabs than a browser on finals week.)

What just happened: the CRA move that scrambled the playbook

The CRA is a fast-track tool Congress can use to overturn certain federal agency actions. When a CRA “joint resolution of
disapproval” becomes law, the targeted action is treated as having no force or effect. In 2025, Congress
passed, and the President signed, CRA resolutions aimed at EPA actions tied to California’s vehicle programsspecifically
including California’s Advanced Clean Trucks and the Heavy-Duty Omnibus Low-NOx programs.
The White House statement announcing the signatures argued those programs were “fully and expressly preempted” without the
waivers and “cannot be implemented.”

California and a coalition of states responded with lawsuits and public commitments to keep pushing clean-vehicle policy,
while the federal government and some industry groups countered that the CRA disapproval restored Clean Air Act preemption.
Add in additional litigation over how California and manufacturers are behaving under side agreements, and you’ve got a
policy tangle that is very much alive in 2026.

Quick refresher: who regulates heavy-duty emissions, and how?

Heavy-duty emissions policy in the U.S. typically sits on three big pillars:

• Federal EPA standards under the Clean Air Act, including rules for “criteria pollutants” like NOx and
  particulate matter (PM), and separate standards for greenhouse gases (GHGs).
• California’s special authority to seek waivers from federal preemption and set stricter standards for
  new motor vehicles and enginesauthority with deep historical roots.
• Other states adopting California standards (where allowed) instead of federal standards, creating a
  “two-path” market: federal-compliance vehicles and California-compliance vehicles (plus “Section 177 states” that follow
  California).

For heavy-duty vehicles, the practical reality is that manufacturers prefer stability. Designing engines, aftertreatment
systems, and full vehicles isn’t like updating a phone app. It’s closer to designing a skyscraper… while people are already
living in it… and also someone keeps changing the building code.

The rules at the center of the storm

1) California’s Advanced Clean Trucks (ACT): sales targets for zero-emission trucks

California’s ACT regulation is a manufacturer sales requirement: if you sell combustion-engine medium- and heavy-duty
trucks in covered classes, you must also sell an increasing share of zero-emission trucks. By 2035, the
program’s targets reach 55% for Class 2b–3, 75% for Class 4–8 straight trucks, and
40% for truck tractors (with annual step-ups along the way). These percentages matter because they shape
everythingfactory capacity planning, dealer inventory, charging/fueling infrastructure investments, and resale value
assumptions.

In a stable world, ACT becomes a predictable glide path. In a world with CRA disapproval and lawsuits, ACT becomes a
question mark with a purchase order attached.

2) California’s Heavy-Duty Omnibus Low-NOx: a tougher smog-cutting push

NOx (nitrogen oxides) is a major contributor to ground-level ozone and smog, and heavy-duty diesel engines are a big slice
of the pieespecially near ports, warehouses, and highways. California’s Omnibus Low-NOx regulation aims at substantial
NOx reductions over model years 2024–2031, including more stringent standards across a broader range of real-world driving
conditions (think idling, low-load, stop-and-go, and highway operation). California’s program also emphasizes longer useful
life and emissions warranty requirements, recognizing that heavy-duty equipment often stays in service for a long time.

California has described optional low-NOx standards (including an aggressive 0.02 g/bhp-hr level) as a stepping stone to
broader mandatory reductionsabout 90% below certain prior baselinesand has framed the Omnibus approach as
part of its strategy to meet health-based air quality standards in key air basins.

3) The federal baseline still matters: EPA’s heavy-duty NOx rule (2027+) and Phase 3 GHG standards

Even with California’s programs in flux, federal rules still set nationwide expectations:

• EPA’s “Heavy-Duty Engine and Vehicle Standards” final rule (December 2022) tightens emissions
  requirements starting in model year 2027 and is designed to reduce air pollution (including pollutants that contribute
  to ozone and particulate matter) across a wider range of operating conditions and for a longer period during engine
  operation.
• EPA’s “Greenhouse Gas Emissions Standards for Heavy-Duty Vehicles – Phase 3” final rule (announced March 2024)
  sets stronger GHG standards beginning in model year 2027 for vocational vehicles and tractors, using technology-neutral,
  performance-based structures that allow manufacturers to choose their compliance pathway.

The big takeaway: even if one set of rules is stuck in court, fleets and manufacturers still can’t ignore federal
compliance planningbecause production cycles don’t wait for court calendars.

Why CRA disapproval creates “regulatory whiplash”

CRA disapproval is different from ordinary policy changes because it can do two destabilizing things at once:

1. It nullifies the specific agency actionhere, the EPA waiver-related decisions tied to California’s
   programsimmediately changing the legal status quo.
2. It raises a “substantially the same” problemthe CRA is commonly understood to restrict the agency from
   reissuing a new action that is “substantially the same” without new congressional authorization. The catch is that courts
   have not provided a crisp, universally applied definition of “substantially the same,” so regulated industries are left
   guessing how narrow or broad that prohibition may be in practice.

In other words: CRA disapproval can remove a rule today and make the path to “fixing” it tomorrow legally uncertain. That’s
a nightmare for capital planning, and heavy-duty vehicles are nothing if not capital-intensive.

A key complication: are Clean Air Act waivers even “rules” under the CRA?

Here’s where things get especially wonky. The Government Accountability Office (GAO) published “observations” in March 2025
indicating that Clean Air Act preemption waivers and related Notices of Decision were not “rules” for CRA purposes in a
prior GAO decision, describing them as adjudicatory orders and noting CRA exclusions for rules of particular applicability.
That view fueled arguments that Congress couldn’t use CRA procedures to revoke the waivers in the first place.

Meanwhile, the Senate proceeded, and the President signed the disapproval resolutions into law. So the industry is left
with a double uncertainty: (1) what happens to California’s programs right now, and (2) whether courts will uphold the CRA
approach used to get here.

What “in flux” looks like in the real world

Policy uncertainty isn’t an abstract headache; it lands in very specific places:

Manufacturers: product planning, certification, and compliance strategy

Heavy-duty OEMs and engine manufacturers need multi-year lead times. They also manage compliance across different vehicle
classes (delivery vans, refuse trucks, school buses, sleeper tractors) and different powertrains (diesel, natural gas,
battery-electric, hydrogen fuel cell). When state-level programs wobble, manufacturers face tough questions:

• Do we keep ramping up zero-emission truck production at the same pace?
• Do we re-allocate engineering resources back toward internal combustion compliance improvements?
• How do we handle dealer commitments and customer pre-orders made under earlier assumptions?
• What happens to credit markets and pooling strategies if standards diverge again?

And, practically speaking, the answer is rarely “flip a switch.” It’s more like “try not to spill coffee on the control
panel while the plane is in turbulence.”

Fleets: procurement timing and total cost of ownership

Fleets care about reliability, uptime, and cost-per-mile. A regulatory swing can affect:

• Purchase timing: If requirements might tighten, fleets sometimes accelerate purchases; if requirements
  might loosen, some fleets may delay, hoping for lower compliance costs.
• Infrastructure: Charging depots and grid upgrades take time. Uncertainty can slow investmentor force a
  fleet to hedge with mixed infrastructure strategies.
• Maintenance planning: New standards often change service needs, parts inventory, diagnostics, and
  technician training pipelines.

Communities and air quality planning: the stakes behind the spreadsheets

California officials and public health advocates often point to the disproportionate impact of heavy-duty emissions.
Reporting has highlighted that heavy-duty vehicles are a small share of the fleet but can represent a large share of NOx
and diesel particulate pollutionespecially in freight corridors and disadvantaged communities. The health benefits
associated with deep NOx reductions are frequently framed in terms of fewer illnesses and improved air quality.

Litigation and enforcement: why courts may decide the next chapter

After the CRA disapproval, the fight moved quickly to the courthouse.

• California and allied states sued to challenge the legality of using the CRA to revoke the waivers and
  to protect California’s long-running authority to set stricter vehicle standards.
• The Department of Justice sued California in August 2025, arguing that, without the waivers, California
  cannot enforce the heavy-duty truck regulations and accusing the state of trying to “circumvent” Clean Air Act
  preemption through the Clean Truck Partnership.
• Industry disputes layered onincluding disagreement over what obligations manufacturers have under
  voluntary or negotiated agreements designed to manage compliance and market transition.

The result is a scenario where “the rules” are not just what’s printed in the Federal Register or a state code, but what
judges decide those rules meanand whether the process used to create or nullify them was lawful.

Scenario planning: three plausible paths from 2026 to 2028

Nobody can responsibly promise how the courts will land. But fleets and manufacturers still need a working forecast. Here
are three realistic planning scenarios:

Path A: Courts rein in the CRA approach for waivers

If courts conclude that Clean Air Act waivers are not subject to CRA disapproval (consistent with GAO’s earlier analysis),
the waiver rescissions could be invalidated. That would likely restore California’s ability to implement programs like ACT
and Omnibus (subject to any additional legal challenges on other grounds). The market would swing back toward a “California
plus adopter-states” compliance trajectory.

Path B: Courts uphold the CRA disapproval

If courts uphold the CRA approach, California’s ability to enforce these particular programs through waiver-based
authority could remain blocked. That could reshape state policy toward alternative tools: incentives, fleet procurement
rules with different legal hooks, in-use programs, and creative funding mechanisms. Manufacturers could see a slower ZEV
ramp in some marketsbut still face federal standards and global decarbonization pressure.

Path C: A split decision with a patchwork aftermath

The most common outcome in complex regulatory litigation is “some of Column A, some of Column B.” For example, courts might
treat different EPA actions differently, or allow certain state measures while blocking others. That would preserve the
uncertainty longerand keep compliance teams living on energy drinks and calendar invites.

What fleets and manufacturers can do now (without pretending we’re your lawyers)

While legal fights play out, practical risk management looks like this:

• Keep federal compliance front and center: EPA’s heavy-duty standards (NOx for 2027+ and GHG Phase 3)
  still shape national product plans and procurement decisions.
• Build flexible procurement contracts: Where possible, include delivery timing options, spec change
  clauses, and performance guarantees that account for regulatory shifts.
• Invest in “no-regrets” infrastructure upgrades: Depot electrical capacity, energy management systems,
  and maintenance training often pay off even in mixed-fleet strategies.
• Use scenario budgeting: Model a “fast ZEV ramp,” a “slow ramp,” and a “patchwork” case, and stress-test
  cash flow and utilization assumptions.
• Track enforcement signals: Litigation outcomes are critical, but so are agency guidance, enforcement
  priorities, and state implementation choices during the interim.

Bottom line

Heavy-duty vehicle emissions rules are in flux because the CRA disapproval resolutions changed the legal footing for
California’s waiver-based truck programs, while courts, agencies, and states continue fighting over what that change
legally means and how far it reaches. Meanwhile, federal standards continue moving forward, technology continues
evolving, and fleets still need trucks that work every Monday morningregardless of what happened on Capitol Hill.

In a perfect world, emissions policy would be predictable enough that businesses compete on engineering and service, not on
guessing what the rulebook will say next quarter. Until then, the best strategy is disciplined scenario planning: assume
change, price uncertainty honestly, and stay ready to pivot without panic.

Field Notes: of “Experiences” from the Heavy-Duty Front Lines

When people say “rules are in flux,” it can sound like a think-tank phrase that floats above the real world. But talk to
the folks who actually buy, build, maintain, or regulate heavy-duty vehicles, and you’ll hear a different vocabulary:
backorders, lead time, spec lock, charger trenching, and what do you mean the timeline changed?

Consider a regional food distributor running a few dozen Class 8 tractors and a larger set of medium-duty delivery trucks.
They’re not trying to “win climate policy.” They’re trying to deliver yogurt to grocery stores without the yogurt turning
into soup. Their operations team planned a gradual rollout of new trucks over several model years, aligning purchases with
driver routes, depot upgrades, and maintenance training. The CRA action didn’t just change a rule; it changed the
assumptions behind their capital plan. Suddenly, the question wasn’t only “Which trucks are best?” but “Which trucks will
be easiest to buy, insure, service, and resell under whichever policy survives?”

Or take a city transit agency. They may already be committed to low-emission or zero-emission buses because riders,
neighborhoods, and public health goals push them there. But procurement cycles are long, budgets are public, and
infrastructure projects have to be permitted and built. When rules wobble, vendors wobble, toosometimes pausing a product
expansion, sometimes shifting allocations between states, sometimes changing price expectations as compliance strategies
evolve. The transit team’s experience becomes less “choose between diesel and electric” and more “choose between
uncertainty today and uncertainty tomorrow, and also make sure we don’t miss the federal grant deadline.”

On the manufacturer side, compliance teams often describe these moments as “parallel universes.” In one universe, state
programs like ACT and Omnibus remain fully in force and expand with adopter states, pushing higher near-term ZEV sales and
aggressive NOx reductions. In another universe, those particular programs are constrained, shifting the near-term market
signalwhile federal standards and customer sustainability commitments still keep pressure on innovation. Engineers, product
planners, and dealer networks are forced to design strategies that can survive in both universes. That means more modular
product architecture, more flexible manufacturing, and (quietly) more meetings that begin with “Okay, worst-case scenario…”

The maintenance world feels it, too. New emissions standards can change aftertreatment systems, diagnostics, warranty
processes, and technician training requirements. Shops invest in tools and training based on what they expect to see in the
field. When the policy picture becomes murky, some shops delay investment; others double down because they see the trend as
inevitable. Either way, the lived experience is the same: the industry keeps moving, but planning becomes harder, and the
cost of being wrong goes up.

That’s the human side of “in flux”: not panic, but constant recalculationtrying to make durable decisions in a world where
the rules can change faster than a truck order can be delivered.

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