DOT Sets 34.9 MPG Fuel Economy Standard for 2031

The Department of Transportation finalized a rule on Sept. 28 setting the country's Corporate Average Fuel Economy standard at 34.9 miles per gallon for model year 2031, according to Ars Technica. The number sits below even the 40.4 mpg target the first Trump administration set in 2020.

What does the new CAFE rule actually require?

CAFE — Corporate Average Fuel Economy — is the federal formula that sets a sales-weighted fuel economy average each automaker's fleet must hit, calculated separately for passenger cars and light trucks. The new notice of final rulemaking pegs that fleet-wide average at 34.9 mpg by model year 2031, per Ars Technica's review of the document. Transportation Secretary Sean Duffy signaled the direction in January, telling automakers that fuel efficiency standards written under the Biden administration were "dead and buried," according to the report.

How does 34.9 mpg compare with earlier standards?

The rollback reaches further back than Trump's first term. In 2012, the Obama administration published CAFE standards aimed at 54 mpg by 2025. That number was never reached: the first Trump administration cut the model year 2026 target from 46.7 mpg to 40.4 mpg in a 2020 rule, and the Biden administration later tightened standards again, according to Ars Technica. The new rule's 34.9 mpg figure for model year 2031 falls below all three prior benchmarks.

By the numbers

• 54 mpg — target set for 2025 under 2012 Obama-era CAFE rules
• 40.4 mpg — model year 2026 standard set by the first Trump administration in 2020, down from a prior 46.7 mpg target
• 34.9 mpg — new model year 2031 standard under the rule finalized Sept. 28

What happens to emissions credits and plug-in vehicles?

Under current CAFE rules, automakers that beat their standards earn emissions credits they can bank or trade to offset years when they fall short. The new notice of final rulemaking criticizes that credit system, arguing it let automakers avoid investing in cleaner engine technology, and eliminates the credits starting in model year 2028, per Ars Technica.

The rule also strips plug-in vehicles from an automaker's fleet average calculation. Previously, an EV or plug-in hybrid could carry a CAFE rating of "hundreds of mpg," pulling a company's overall average up, according to the report. Without that boost, Ars Technica notes automakers may drop EV and PHEV models from their lineups entirely rather than build vehicles that no longer help them meet the standard.

Why is the light truck classification changing?

CAFE has long treated passenger cars and light trucks as separate categories, with looser standards for light trucks. That gap pushed automakers to redesign crossovers so they would qualify as light trucks rather than cars, filling American roads with larger, thirstier SUVs, per the report.

The new rule tightens that loophole — if it remains in effect through model year 2030. The Department of Transportation's language, as quoted by Ars Technica, states the rule will:

"change classification criteria starting in model year 2030 to reflect each vehicle's intended use accurately, flipping the current fleet mix of approximately 70 [percent] light trucks and 30 [percent] passenger vehicles to around 70 [percent] passenger cars and 30 [percent] light trucks."

Has DOT been enforcing the existing CAFE rules?

Enforcement had already gone slack before the new rule. In July 2025, the department told automakers it would not fine any manufacturer for exceeding CAFE limits going back to 2022, according to Ars Technica. That signaled the administration's approach months before the formal rulemaking landed.

What to watch next

• Whether individual automakers announce cuts to EV and plug-in hybrid lineups ahead of the model year 2028 credit elimination
• Whether the light truck reclassification survives without amendment through model year 2030
• Legal challenges from states or environmental groups to the final rule
• Consumer fuel costs, which Ars Technica notes are climbing as the rollback takes effect

Read the original reporting at Ars Technica.