The world's new cars could use half as much as much fuel as they do now in 20 years, if current technologies are more widely adopted, according to the International Energy Agency.

In a pair of reports issued Wednesday the agency said with aggressive new policies, the world could stabilize its oil consumption even if the number of vehicles on the road doubles by 2050. Without those policies, cars and trucks would consume twice the amount of oil they do today.

Half the world's oil — about 45 million barrels per day — is used to make the gasoline, diesel and jet fuel needed to drive, ship or fly.

The IEA, an energy security group with 28 oil-importing member countries, suggested a number of policies and technologies that could lead to far less fuel use. Many are already being adopted around the world, but the agency said the pace of change could be accelerated.

IEA pointed to better labeling of fuel economy and carbon dioxide emissions of new cars, and standards that mandate minimum fuel economy levels and limit carbon dioxide emissions. It also suggested taxes or other financial measures that penalize buying gas-guzzlers and reward the purchase of fuel-efficient vehicles.

Last month the Obama Administration finalized regulations that will force automakers to nearly double the average gas mileage of all new cars and trucks they sell in the U.S. by 2025.

Energy industry executives and government forecasters say U.S. gasoline demand peaked in 2006 and will slowly decline because of more fuel efficient cars and trucks and demographic changes. Similar trends are playing out in Western Europe and Japan. But millions of people in the developing economies of China, India and elsewhere are buying cars for the first time and pushing up world oil demand.

The technologies needed to keep a lid on that demand growth are available today, including more efficient transmissions, lighter materials, hybrid-electric vehicles, better aerodynamics and more efficient lights, heaters and air conditioners. According to one of the IEA reports, many of these technologies are already cost-effective — the fuel savings outweigh the added costs over the life of the vehicle — but they are not yet adopted widely enough.

The agency said further improvements in lightweight materials, low-friction lubricants and waste-heat recovery systems are needed to improve fuel economy even more in the years ahead.

Only about 20 percent of the energy in a gallon of gasoline is actually used to propel a vehicle. Much of the rest is wasted in friction and heat.

Road vehicles consume about 75 percent of the energy used worldwide for transportation, and transportation is responsible for 20 percent of the world's total energy consumption, the agency said. Fuels made with crude oil such as gasoline, diesel and jet fuel dominate the transportation sector.

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