"I only use my car in town," she says. "We bought a diesel car deliberately because it is cheaper to run."
That is partly because the French government encourages the use of more- efficient diesel fuel by taxing it less heavily. Only in four European countries is diesel more expensive than gasoline, the way it is in America.
But efficiency alone does not explain the huge disparity between fuel-use figures on either side of the Atlantic: European per capita consumption of gas and diesel stood at 286 liters a year in 2001, compared to 1,624 in the US, according to IEA figures.
The nature of cities plays a role, too. "America has built its entire society around the car, which enabled suburbs," points out Mr. Dings. "European cities have denser centers where cars are often not practical."
In Paris, for example, about half the trips people make are by foot, by bicycle, or on public transport, says UNEP's Mr. Fulton. In America, that figure is more like 20 percent.
"The single most effective measure" that has brought down motorists' fuel use in Europe, however, is taxation, says Dings.
On average, 60 percent of the price European drivers pay at the pump goes to their governments in taxes.
In Britain, the government takes 75 percent, and raises taxes by 5 percent above inflation every year (though it has forgone this year's rise in view of rocketing oil prices, and the French government has promised tax rebates this year to taxi drivers, truckers, fishermen, and others who depend heavily on gasoline.) On August 8, for example, the price of gas in the US, without taxes, would be $2.17, instead of $2.56; in Britain, it would be $1.97, instead of $6.06.
"There is really good evidence that higher prices reduce traffic," says Stephen Glaister, a professor of transportation at London's Imperial College. "If fuel prices go up 10 percent ... fuel consumed goes down by about 7 percent, as people start to use fuel more efficiently, not accelerating so aggressively and switching to more fuel-efficient cars. It does change people's behavior."