Clean Air Act Regulatory Framework for Mobile Sources
The Clean Air Act generally reserves the authority to regulate emissions from mobile sources such as cars, trucks, locomotives, and nonroad equipment at the federal level (i.e., by the U.S.EPA only). Individual states and local governments are thereby preempted from adopting and enforcing their own standards on the basis that differing rules and engine certification standards, applied over a large geographic area, would create an unworkable patchwork of requirements for engine and equipment manufacturers.
An exception is made for the State of California, due to its early adoption of its own vehicle standards since the 1970s, and California’s unique air quality challenges. California may adopt its own standards (and other states may adopt California’s rules by reference thereafter), but only after EPA finds that California’s rules are reasonable and necessary, and not at odds with federal rules. EPA has routinely approved California’s mobile source emission rules by issuing “waivers” of preemption for each new rule following petitions by the California Air Resources Board (CARB).
CARB’s Aggressive Mobile Source Programs and EV Ambitions
Since the mid-2000s, CARB’s mobile source regulations have become increasingly more complex. Prior manufacturer engine and vehicle certification requirements were supplemented with end user “fleet rules” that required equipment owners to accelerate the turnover of older, higher-emitting vehicles and engines, or to retrofit them with aftermarket add-on controls.
In 2020, CARB was further emboldened by Governor Gavin Newsom’s Executive Order N-79-20 that seeks to eliminate the internal combustion engine from California commerce by 2035, in favor of zero emission vehicles or “ZEVs” (battery electric vehicles and hydrogen fuel cell vehicles). This prompted CARB’s Advanced Clean Cars II and Advanced Clean Trucks Regulations, establishing manufacturer sales targets for ZEVs. CARB went one step further with its Advanced Clean Fleets Regulation, which mandated that certain larger and government fleets purchase the ZEVs required to be sold by Advanced Clean Trucks Regulation. In this way, CARB attempted to control both the manufacturer and purchaser sides of certain vehicle sale transactions in California.
Additionally, CARB adopted an In-Use Locomotives Regulation aimed at assessing an operating fee for nearly all locomotives in the state. The fee was envisioned to fund spending accounts for each railroad’s future purchase of emerging-technology battery-electric and hydrogen locomotives. This approach diverged significantly from CARB’s historic approach to locomotive emissions through negotiated memoranda of understanding (MOUs) with railroads. The prior approach was based on the position that the Clean Air Act did not allow for direct regulation of emissions from new locomotives.
Recent California Waiver Activity
The run-up to the change in federal administration on January 20 saw a number of CARB’s waivers not yet acted-upon by EPA. On January 6th, 2025, U.S.EPA published their decision to approve the Advanced Clean Cars II regulation in full, which requires that 100% of light-duty cars, trucks, and SUV sales in California be zero-emissions by 2035.
However, on January 10, 2025, EPA published a decision only partially approving CARB’s waiver request with respect to its Transportation Refrigeration Units (TRU) Rule. EPA decided to approve CARB’s lower engine emission standards but declined to act on the zero emissions (ZE) elements of the TRU Rule.
In response, on January 13, 2025, CARB requested the withdraw of their waiver requests for their Advanced Clean Fleets Rule (ACF) and In-Use Locomotives Rule. Both of these rules were the result of a multi-year CARB adoption process. Following approval, both attracted litigation from their respective regulated industry sectors.
Regarding CARB’s recently approved Advanced Clean Cars waiver, the new Trump Administration has already stated, “California has imposed the most ridiculous car regulations anywhere in the world, with mandates to move to all electric cars,” … “I will terminate that.” In response, CARB’s Board Chair Liane Randolph stated, “Frankly, given that the Trump administration has not been publicly supportive of some of the strategies that we have deployed in these regulations, we thought it would be prudent to pull back and consider our options.”
Implications of the Action
The fallout of CARB’s waiver withdrawal request is yet to be seen. CARB will likely allow the two rules to remain “on the books” as part of the California Code of Regulations, until perhaps a subsequent, friendlier administration is in power. The fate of the ongoing litigation is also uncertain. Will judges dismiss the current cases as unripe, or will they allow the respective complaints to progress? It is probable that other states that had ambitions of adopting CARB’s ACF regulation will delay or cease their efforts—Oregon, Washington, Colorado, and New Mexico.
What is certain is that the U.S.EPA waiver authorization process for California mobile source rules will become increasingly more political. CARB will not be able to rely on federal “rubber-stamping” of their programs, and especially those that require ZEV mandates. This may be a relief to the regulated community who has long accused CARB of establishing aberrant and anti-commerce requirements.
For more information on this topic, please contact Allan Daly by email or at 916.273.9980
