The rules are intended to improve fuel economy and reduce emissions from tractor-trailers and other large vehicles that transport steel, cars, oil and a wide array of consumer products. It will be up to engine and truck-tractor makers to determine how to meet them.

Analysts have estimated the cost of complying with the new standards at $12,000 a vehicle. Mr. Foxx said those investments would be outweighed by larger economic gains such as reduced fuel consumption.

“This is going to be a huge economic opportunity for those who are in the trucking industry,” he said.

The American Trucking Associations, the road-cargo industry’s largest trade group, said it was cautiously optimistic that the new standards could be met without causing disruption to vehicle manufacturers and corporate fleets.

“While the potential for real cost savings and environmental benefits under this rule are there, the fleets will ultimately determine the success or failure of this rule based on their comfort level purchasing the new technologies,” said Glen Kedzie, an association official.

Heavy-duty trucks are the fastest-growing segment of the American transportation sector in terms of fossil-fuel consumption and account for about 20 percent of greenhouse gas emissions, despite making up only 5 percent of the vehicles on the road.

The Obama administration has already mandated big increases in fuel economy for passenger cars and trucks. The government recently affirmed its target of 54.5 miles per gallon as a fleetwide average by 2025.