One of two fuel-economy label designs proposed by the U.S. federal government assigns a letter grade based on comparisons across the nation’s light-vehicle fleet with no consideration for segmentation.

The grade range unveiled today by the Environmental Protection Agency and the Department of Transportation starts at A+ and descends to D. The top mark is reserved for electric vehicles while the bottom ranking likely will be the providence of gasoline-powered high-performance vehicles.

The proposed rule features examples based on ’10 model-year data. Most light trucks were crowded between B and C-.

Light trucks accounted for 49.8% of the U.S. market through July, up from 48.2% for full-year 2009, according to Ward’s data.

“We’re not looking at letter grade as a judgment,” Gina McCarthy, EPA assistant administrator-air and radiation, tells journalists during a teleconference.

But the proposed rule-making – which would take effect in model-year ’12 – also says additional text on the label “will indicate which vehicles are the ‘best,’ thus, meeting the requirement that the label designate highest fuel economy and lowest greenhouse gas vehicles.”

The second proposed label highlights combined city-highway fuel economy and an estimated annual fuel cost. It also accounts for segmentation.

“There is no preferred option,” says National Highway Traffic Safety Admin. Administrator David Strickland. “We’re asking for comment.”

And while auto makers are welcome to provide comment as “key stakeholders,” the final decision will be “up to the public,” McCarthy says.

In conjunction with feedback from 256 focus group participants in Seattle, Houston, Chicago and Charlotte, NC, the letter-grade proposal was developed following “a day-long consultation with an expert panel of individuals who have introduced new products or have spearheaded national educational campaigns,” says the proposed rule-making notice.

Their strongest recommendation, the document adds: “Keep it simple.”

But the Alliance of Automobile Manufacturers urges caution.

“We’ve said this for years: ‘Whenever you’re trying to summarize information, you always lose something,’” warns spokeswoman Gloria Bergquist. “It’s very difficult to rate a complex vehicle like you would a movie.

“We know the agency has done ‘stars on cars,’ and that provides one source of information. But when you start looking at letter grades, it carries a connotation of passing and failing from our schoolyard days.

“It’s such a value judgment it becomes a government stamp of approval, and I don’t think that’s the intention,” she adds. “Let consumers arrive at their own opinions.”

The proposed rule-making says the EPA and DOT are “hopeful that a rating system as simple as a letter grade may encourage consumers to rely more on the rating system itself in making purchasing decisions, rather than on, for example, (miles-per-gallon) numbers.”

Focusing on mileage, creates an “MPG illusion,” the document warns, referring to the mathematical disparity between miles per gallon and gallons per mile.

“Even if consumers clearly understand that higher MPG is better, those comparing vehicles with relatively low MPG values may not know that MPG differences that appear to be small, even one or two MPG, may actually have very different fuel consumption values,” the document says.

“And that selecting the slightly higher MPG vehicle could actually result in significantly less fuel used, thus saving a considerable amount of money.”

Europe and Canada use this metric to rate the fuel economy of their fleets.

“(The current U.S.) petroleum-centric labels simply are not good enough anymore,” Strickland tells reporters.

Using ’10 model-year data, 1,245 vehicles scored in the B range; 735 vehicles were in the Cs; 17 were rated A- or higher, while 14 garnered a D or D+.

The letter-grade labels also feature estimated savings in dollars, based on a vehicle’s performance rating.

To evaluate plug-in hybrid-electric vehicles, the EPA and DOT proposes translating electricity consumption into a miles-per-gallon equivalent, while EV energy use will be expressed in kilowatt-hours per 100 miles (161 km).

– with Byron Pope