WASHINGTON -- The federal government formally proposed last month the first regulations designed to limit fuel consumption of larger commercial vehicles -- from over-the-road buses to big-rig trucks - saying the rules address the thirstiest and most-polluting vehicles on the road.

The proposal, which would take effect with 2014 models and ratchet up through 2018 models, requires a public comment period and other procedures, and wouldnt be final until next year.

President Obama announced in late May that the USEPA and National Highway Traffic Safety Administration would team up to create the proposed rules. (See June 1 Bus & Motorcoach News.)

The rules would raise the cost of buses, trucks and the diesel engines most of them use, but the government says the payback in fuel savings would be as fast as one year for heavily used over-the-road commercial vehicles.

The National Research Council, which issued a report earlier this year that formed the backbone of the proposed rule, said that advanced technologies could lower fuel consumption in motorcoaches by up to 32 percent by 2020. (See May 15 Bus & Motorcoach News.)

However, achieving the improved fuel economy would cost an estimated $36,350 per bus, according to the report, which said it would be a cost-effective expense if the price of fuel is $1.70 per gallon or higher.

Even higher fuel prices would make the investment even more cost effective, said the report. Diesel fuel currently averages just over $3 per gallon nationwide.

The complex proposal would cut fuel use 10 to 20 percent, according to federal estimates.

Major trucking interests endorsed the move for its potential cost savings. The American Trucking Associations noted that it has backed fuel-consumption regulations since 2008. "The proposal, using current technology, is achievable," spokesman Brandon Borgna said.

A consortium representing drivetrain, trucking and shipping companies says it recommended fuel-use regulations for commercial trucks as far back as 2006. Now called the Heavy-Duty Fuel Efficiency Leadership Group, it "devised a set of principles" for big-truck fuel use and proposed them to the Obama administration this year.

Although the emphasis is on large commercial vehicles, the regulations also would apply to vehicles as small as those with an 8,500-pound gross vehicle weight rating (the safe weight of the truck and cargo combined) - a Ford F-250 pickup or equivalent.

The government forecast the rules would cost industry $7.7 billion, but save $35 billion in fuel.

The standards would apply to the manufacturers of both engines and vehicles, not to the companies that use them.

Navistar, which builds buses and big trucks and the engines that power them at its IC Bus and International Truck and Engine unit, says its too soon to determine the precise effect of the proposed rules, but hopes the government will "properly incentivize" advanced technologies. Navistar makes fuel-saving diesel-electric hybrid systems for buses and commercial trucks.

Critics say the standards might not be high enough and should "do more to draw advanced technologies into the market" by giving added credit for hybrid drivetrains or advanced transmissions, says Therese Langer, head of transportation issues at the American Council for an Energy-Efficient Economy, an advocacy group.

"With just five years of new vehicles sold under this program, America will eliminate the same amount of oil that we import from Russia and Nigeria in a year," said Rep. Edward Markey, D-Mass., member of several energy-related House committees.