WASHINGTON – If motorists used rechargeable “plug-in” hybrid-electric vehicles in large numbers, the U.S. could see a significant drop in greenhouse gas emissions by the middle of the century, says a study released Thursday.

Researchers estimated that with a market share of about 60 percent or more plug-ins, the vehicles could help reduce approximately 450 million metric tons in greenhouse gas emissions a year by 2050. The reductions would be the equivalent of removing 82 million passenger cars, or about one-third of the cars currently on the road.

The study was conducted by the Electric Power Research Institute, a nonprofit research group, and the Natural Resources Defense Council, an environmental group. It was based on an analysis of data from the federal Energy Information Agency and EPRI.

“Plug-in hybrids are a major solution to the climate change crisis that we’re facing and the electric utility industry is indeed capable of taking over a large section of the fueling transportation sector without adding significant new capacity,” said John Duncan, deputy general manager of Texas-based Austin Energy.

Researchers said a significant increase in plug-ins would lead to only a minor increase in demand for electricity. An increase of 7 percent to 8 percent of electric use would reduce nearly 4 million barrels of oil per day by 2050, said Mark Duvall, program manager with the Electric Power Research Institute and one of the study’s authors.

The study estimated that with a more limited use of plug-ins, or about 20 percent of the market, the vehicles could remove approximately 180 million metric tons of greenhouse gas emissions a year by 2050.

A separate study by the organizations found that plug-in vehicles also could lead to small improvements in the nation’s air quality. Most regions of the country would see improvements in ambient air quality and the reduction of pollutants, they found.

Plug-in hybrids are being developed by several automakers, including General Motors Corp., Ford Motor Co., DaimlerChrysler AG and Toyota Motor Corp. The vehicles typically feature batteries that power an electric motor with an internal combustion engine used when the batteries run low.

Owners plug the batteries into a standard wall outlet to recharge it, typically at night. The study assumed that three-quarters of the charging would take place at night during the off-peak hours of the electric grid.

A number of obstacles persist for plug-ins. Automakers and battery companies have been working to improve the durability of the batteries, improve the vehicle’s range and assess the impact that wide use of the vehicles would have on the nation’s electric grid.

Conventional hybrid gas-electric vehicles, such as the Toyota Prius, comprise only about 2 percent of the vehicle market. General Motors, which is developing the Chevrolet Volt, a plug-in electric car with a range of 40 miles on the battery and more than 600 miles with a gas engine, has said it hopes its plug-ins can reach showrooms by 2010.

Tony Posawatz, GM’s vehicle line director, said the automaker expected to begin testing advanced batteries from suppliers in coming months that could be used in the Volt.

The study was funded by a broad number of interests, including investor-owned utilities, public power agencies, state and federal agencies, public interest groups and foundations, said Steven Specker, EPRI’s president and chief executive officer.

On the Net:

Electric Power Research Institute: http://www.epri.com

Natural Resources Defense Council: http://www.nrdc.org/

A service of the Associated Press(AP)