(Bloomberg) -- U.S. regulators have underestimated the costand difficulty of achieving their vehicle fuel-economy andgreenhouse-gas targets for 2025 and are giving California too muchpower to shape the country’s policies on those issues, an automakergroup said.

Even with the current government estimate of $1,800 a vehicle inadded costs, “the payback period for alternative technologiesextends beyond the timeframe most consumers consider; it is likelyto remain that way,” the Alliance ofAutomobile Manufacturers said in a report posted on its websiteMonday. Members of the Washington-based lobbying group includeGeneral Motors Co., Ford Motor Co., Fiat Chrysler Automobiles NV,Toyota Motor Corp. and Volkswagen AG.

The alliance is seeking to influence the upcoming midtermevaluation by regulators of the 2011 plan by President BarackObama’s administration to boost the fuel economy of cars and lighttrucks by 54% to a projected 54.5 miles (87.7 kilometers) pergallon by 2025 and cut tailpipe carbon dioxide emissions by 35%.The review is meant to consider whether changes are needed in theplan based on actual performance so far.

The U.S. Environmental Protection Agency, the National Highway TrafficSafety Administration and the California AirResources Board are preparing for the midterm evaluation, withthe three agencies set to issue a draft technical assessment reportlate this month or in early July.

Nick Conger, an EPA spokesman, didn’t immediately respond to arequest for comment on the alliance report. In December,Christopher Grundler, the EPA director of air quality andtransportation, said in a report that average fuel economy hasimproved by 5 mpg, or 26%, in the last 10 years, more than expectedand that “it’s clear our standards are working.”

Hybrid estimates

The automaker group said an EPA projection in 2012 that meeting the2025 federal mileage standard would need only 5% of U.S. cars andlight trucks to be hybrids is too low. A recent analysis done forautomaker groups found that as many as 47% of all cars may need tobe as fuel efficient as current hybrids, the alliance said.

“The actual cost of the program depends on this projectedtechnology mix,” the alliance said.

Lower gasoline prices affect sales of hybrids and the mix ofcars and light trucks, the automaker group said. Consumers may beopting for gasoline-powered vehicles because reduced fuel priceshave extended how long it would take to recoup the higher costs ofalternatives such as hybrids, the alliance said.

To meet the targets, automakers will have to boost fuelefficiency by almost 67% in the 13 years ending in 2025, comparedto 23% in the nine years ending in 2014, the alliance said. Thatacceleration may not be realistic, according to the group.

California effect

The automaker group also cited the impact of Californiarequirements, adopted by nine other states, that by 2025 aprojected 15.4% or more of new-vehicle sales be zero-emissionsmodels, powered by batteries or fuel cells. In addition, whenCalifornia issues its own assessment in November on whether thestate’s CO2 targets for 2022-2025 should be maintained, it will bejumping ahead of the midterm evaluation and exerting adisproportionate impact on the national debate, according to thealliance.

Ceres, a Boston-based coalition of investors andenvironmentalists, said in a statement Monday that higherfuel-economy targets will protect automakers from future oil priceshocks.

“U.S. automakers have been caught flat-footed before,’’ saidCarol Lee Rawn, director of the Ceres transportation program.

The InternationalCouncil on Clean Transportation, a nonprofit advocacy group,said this week that without higher fuel-economy targets in the U.S.and other countries, global oil demand could grow from 94 millionbarrels a day in 2015 to 112 million by 2030. If the U.S. and othercountries maintain the targets, oil demand could level off at 101million barrels a day by 2030, the group said.

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