Looser Fuel Economy Rules Could Grow Automakers' Scope 3 Emissions, Not Shrink Them

Washington has made it cheaper to build a less efficient car. It has not made the car's emissions disappear. The National Highway Traffic Safety Administration's new fuel economy rule lowers what automakers must achieve, but every extra gallon burned by the vehicles they sell still lands in the place their climate reporting is most exposed: Scope 3, Category 11, the use of sold products. That ledger is the one California will require them to disclose from 2027.

What the Final Rule Actually Changes

The rule was published in the Federal Register on September 30 and takes effect November 30, according to an analysis in The National Law Review. For model year 2031 it corresponds to 40.2 mpg for passenger cars, 26.4 mpg for light trucks and 34.9 mpg across the fleet. The standards are set on what gasoline, diesel and non-plug-in hybrid technology can achieve, with electric vehicles excluded from the calculation. Civil penalties for falling short have already been set to zero under the One Big Beautiful Bill Act, and EPA's separate greenhouse gas standards are untouched by this rule.

The structural changes may matter more than the headline number. As GoodCarBadCar details, credits earned from model year 2028 onward can no longer be traded between manufacturers, and from model year 2030 a vehicle with a fold-flat third row no longer qualifies as a light truck. The agency counts 68 percent of today's light-duty fleet as meeting the truck definition, so the reclassification reaches well beyond a niche segment.

NHTSA's own numbers frame the tradeoff. It estimates the rule cuts compliance technology costs by $15.3 billion through 2031, or about $1,289 per vehicle, while raising gasoline spending by more than $1,600 over a vehicle's lifetime, per a summary from Hashtag Investing. It also projects U.S. gasoline consumption 4.6 percent higher through 2050 than under the prior path.

Why the Extra Fuel Lands in Scope 3

For a carmaker, the factory is not the main event. A University of Michigan Center for Sustainable Systems project conducted with Ford found that value chain emissions represent over 90 percent of an automaker's total inventory, with tailpipe emissions from vehicles sold as the dominant source, as The Auto Wire reported. Category 11 counts the expected lifetime emissions of every vehicle sold in the reporting year, so a fleet that burns more fuel per mile carries a larger number from the day it ships. The Science Based Targets initiative's land transport guidance, covered by Supply Chain Dive, already treats Category 11 as the largest source of automaker emissions, and private cars and vans account for roughly 10 percent of global energy-related carbon emissions.

Federal retreat on reporting does not change that math either. The same Auto Wire report notes that EPA quietly removed its Scope 3 guidance from its Corporate Climate Leadership website. California's SB 253 still requires companies with more than $1 billion in revenue doing business in the state to disclose Scope 1 and 2 emissions in 2026 and Scope 3 from 2027, which captures every major automaker and many large suppliers. European rules impose similar obligations.

None of this means emissions must rise. A manufacturer can keep building efficient vehicles regardless of the federal floor. But the rule removes two pressures that pushed in that direction: a penalty for missing the target and a market for selling surplus credits. Automakers with large EV portfolios have historically sold credits to rivals that fell short. Under the new rule, that market closes for credits earned from 2028, so the efficiency now has to justify itself through product strategy and disclosure, not compliance revenue.

A Split Rulebook Runs Through the Supply Chain

The rule was signed September 25 with support from the Alliance for Automotive Innovation, General Motors, Ford and Stellantis, while the Sierra Club, the Center for Biological Diversity and the American Lung Association vowed to fight it, according to Nature World News. Challenges are expected to argue the standards fail the statutory test of maximum feasible efficiency.

Meanwhile Canada is developing its own greenhouse gas standards for model years 2027 to 2032, intended to tighten over time, and more than 90 percent of Canadian-made vehicles are exported to the United States. That leaves suppliers building to one regulatory path for some customers and a different one for others, with the product mix shifting under multiyear supply agreements written for the old rules. Contract terms covering volumes, powertrain mix and emissions data are where that divergence will be absorbed.

Automakers and suppliers getting ahead of the gap are working through a short list:

• Model Category 11 under the new standard. Run 2027 to 2031 sales plans through the lower fleet targets to see how much use-phase emissions could rise before California reporting makes the number public.
• Separate compliance from disclosure. Meeting a 34.9 mpg target with a zero penalty says nothing about Scope 3; brief the board that the two now point in different directions.
• Reprice the credit strategy. Credits earned through 2027 stay tradable, but plans that count on selling credits from 2028 onward need to be rebuilt without that revenue.
• Review supplier agreements for powertrain mix. Identify contracts tied to EV or hybrid volume assumptions and the clauses that govern renegotiation if the mix changes.
• Collect product-level efficiency data now. Category 11 estimates depend on fuel economy and lifetime mileage assumptions per model, so tighten that data before assurance arrives.
• Plan for two markets. Map which vehicles and parts serve both the U.S. and Canada, and where diverging standards would force separate specifications.

The federal rule lowers a compliance bar. It does not lower the emissions that investors, California regulators and European rules will ask automakers to count. Companies that treat the rollback as relief may find the bill arriving a year later, in a Scope 3 disclosure with their name on it.