Hours after being sworn in as the new U.S. Secretary of Transportation, Sean Duffy took aim at the main way the federal government regulates miles per gallon for cars and pickup trucks — also a principal way that it regulates air pollution and addresses climate change. Duffy ordered the federal agency in charge of fuel economy standards to reverse them as soon as possible. The standards have been in place since the 1970s energy crisis and were intended to conserve fuel and save consumers money at the gas pump.

Here are five reasons why the action matters.

Duffy ordered his chief of the National Highway Traffic Safety Administration to “propose the rescission or replacement of any fuel economy standards” necessary to bring the rules in line with Trump’s priority of promoting oil and biofuel.

The order came in a DOT memorandum Tuesday night. Duffy said the rules need to better align with the administration’s overarching agenda because “the existing CAFE standards promulgated by NHTSA are contrary to Administration policy.”

Duffy says eliminating the rules will increase Americans’ access to the full range of gasoline vehicles they need and can afford.

Others disagree. “This will raise consumer’s costs at the pump, increase tailpipe pollution and jeopardize U.S. automakers’ future, and no one........

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