The Environmental Protection Agency is expected to propose new rules limiting auto tailpipe emissions this week as part of a plan to accelerate a transition to electric vehicles in the U.S.

Why it matters: Transportation is the country's largest source of greenhouse gas emissions.

• Curbing pollution from vehicles is a crucial aspect of the U.S. pledge under the Paris Agreement to cut emissions by 50% below 2005 levels by 2030.

Driving the news: The EPA is expected to roll out a draft plan setting emissions rules for light-duty vehicles including cars, SUVs and pickups from model years 2027-2032, an agency official told Axios.

• Another draft plan will set rules for heavy-duty vehicles and engines.
• The New York Times reports the regulations would effectively require electric vehicles to account for 54% to 60% of new car sales by 2030 and 64% to 67% in 2032 — though the Washington Post notes these numbers represented the most stringent of several options in the rule.
• The EPA official emphasized to Axios in an email that "the proposal process is not yet final."

By the numbers: President Biden has set a non-binding goal for at least 50% of all new cars sold in 2030 to be zero-emissions models, including electric and hydrogen fuel cell models.

• Major industry group the Alliance for Automotive Innovation noted in a memo published last week in anticipation of the new rules announcement that the EV market share of new vehicle sales reached almost 10% in December as demand increases.

State of play: Automakers including Ford and General Motors have stepped up EV sales drives and other initiatives to combat climate change.

• Ford has pledged to "achieve carbon neutrality" by 2050 "while setting interim targets to more urgently address climate change challenges."
• GM has said it plans to become "carbon neutral" by 2040 while setting a worldwide target to end sales of gasoline and diesel powered cars, pickups and SUVs by 2035.
• But environmental groups say more efforts are needed in tackling tailpipe emissions.

What they're saying: "Tailpipe emissions pollute the air we breathe and worsen severe weather," said Fred Krupp, president of advocacy nonprofit Environmental Defense Fund in a statement welcoming the expected EPA action.

• "The race to cleaner air, a safer climate and more made in America jobs — is on."

Meanwhile, the Alliance for Automotive Innovation said in its memo that a "clear-eyed assessment of market readiness" is required.

• "Regulatory mandates alone will not address the conditions … that will determine the ultimate success of the EV transition," the group added.

Go deeper: More in Axios Generate on Monday

Editor's note: This article has been updated with further context.