The new regulations require state and local officials to measure greenhouse gases from cars and trucks and compare the data over time. (Toby Talbot/AP)

Following a lawsuit by California and seven other states, the Trump administration has reversed course and instituted new regulations requiring that greenhouse gases from cars and trucks be measured and compared over time.

The regulation was published two days before the Obama administration left office and was repeatedly delayed by President Trump's Transportation Department. The transportation sector is one of the top sources of emissions causing global warming.

"The Trump Administration backed down and will now implement the measure as is legally required," California Attorney General Xavier Becerra (D) said in a statement this week. "Climate change is real. If President Trump is not prepared to admit it or to do his job of protecting our families by enforcing our environmental rules, then I'm prepared as Attorney General to call his bluff."

California and the other states — Iowa, Maryland, Massachusetts, Minnesota, Washington, Oregon and Vermont — alleged in the suit, filed last week, that the administration had intentionally and unlawfully failed to give the public the required opportunity to comment on the indefinite delay. Environmental groups had sued over the issue, as well.

U.S. transportation officials declined to address the allegations. The Federal Highway Administration released a statement saying, "We have no objections to states choosing to collect greenhouse gas data, or setting targets for greenhouse gas reduction."

Trump has blamed federal regulations and environmental rules for contributing to what he claims is the United States' "Third World" infrastructure. He has pushed to sharply reduce environmental enforcement and repeatedly rejected the scientific consensus on the dangers of climate change.

Some states and industry groups had objected to the greenhouse gas requirement.

The American Trucking Associations said in July that the "requirement is likely to lead to permitting delays and required mitigations that will add costs and time to projects."

The Utah Department of Transportation also voiced its opposition, saying the Obama-era regulation "exceeds the scope established by Congress" and was an attempt to "advance climate-
related issues that could not be advanced through other legitimate legislative avenues."

In a public notice Thursday describing the reversal, the Federal Highway Administration said it "recognizes that there are short time frames to comply with the October 1, 2018, reporting deadline" but expects that the burden to comply "will be minimal, consisting mostly of preliminary ­target-setting activities using existing data sources."

The rule calls on state transportation departments to come up with a baseline for current carbon-dioxide emissions from all cars, trucks and motorcycles on the national highway system, which includes interstates and some other roads.

States and regional planning officials would then calculate 2017 totals using "motor fuel sales volumes already reported" to Washington, along with figures on emissions per gallon and miles traveled, according to federal documents.

State and metropolitan-area officials would gauge the percentage change over time and be required to "establish targets and report on progress," with the Federal Highway Administration assessing that progress every two years, according to a federal description of the rules.

"Important rules such as this one take a year or so to develop, with adequate comment periods (this one's spanned four months). A new administration can't just willy-nilly decline to follow through," said a blog post from the Natural Resources Defense Council, which along with Clean Air Carolina and the U.S. Public Interest Research Group sued Transportation Secretary Elaine Chao over the matter in July.

But Trump officials have indicated that they expect the setback will be short-lived.

Last month, the Transportation Department said it would launch a new regulatory process to gather additional information and public comments on the greenhouse gas requirement that would aid federal highway officials "in determining whether the measure should be retained, revised or repealed."

But in its notice this week, the administration was more explicit about its intentions, saying the Federal Highway Administration "has initiated additional rulemaking procedures proposing to repeal the [greenhouse gas] measure." It said a formal notice outlining that effort would be published this year, with a goal of putting it into place by spring of 2018 — before the first compliance deadline.

Juliet Eilperin contributed to this report.