ROME — Ten dollars a gallon may seem unthinkable to American drivers still smarting from the spike in gas prices to around $4 a gallon. But that was nearly the price that Marco Annarumi faced recently when filling his Jeep on his way home from work.

"It hasn't changed my driving at all — not a bit — I just have to work harder," he said with seeming indifference.

High oil prices and high taxes on gas pushed the average price of gasoline to new heights in much of Europe this summer. Yet transportation experts in this laboratory of sky-high fuel prices say many Europeans, out of necessity, habit or love, have proved surprisingly willing to bear the extra cost of driving. That raises questions as to how effective high prices by themselves can be in achieving the ambitious targets for reducing carbon dioxide emissions that European leaders have committed themselves to meeting.

Gas prices have persuaded some people to drive less. Traffic on the Eurostar train that links London and Paris was up 21 percent in the first three months of 2008. Gas purchases in Italy dropped 10 percent compared with the year before. Sales of gas-guzzling sport utility vehicles have plunged across the continent, just as they have in the United States.

But, at least so far, there are few signs of the wholesale shift away from current driving habits that environmental economists contend is needed for European countries to meet emissions control targets. The U.N. Intergovernmental Panel on Climate Change says meeting the targets is crucial if the world is to prevent the worst effects of global warming. Rental car companies say their business is up this summer. Many consumers appear willing to economize in other parts of their lives — eliminating vacations, movies, even birthday gifts — before choosing not to drive.

"We do see reports of a significant change in the types of cars people are buying, but I've been mostly surprised at the lack of a reaction," said Peder Jensen, a transportation expert at the European Union's European Environment Agency in Copenhagen. "One had hoped that these prices would deter driving, but people have coped better than we hoped they would."

Although new car sales in both Europe and the United States have slumped this year, the number of cars per person has continued to rise, partly because many people now have more than one car, according to statistics from the Organization for Economic Cooperation and Development.

Partly because of high gas prices here, European cars are already far more efficient than those sold in the United States. The average new European car gets 40 miles to the gallon, double the average for new cars sold in the United States. Even so, total carbon emissions from all forms of transportation in Europe are rising. They are about a quarter higher today than they were 20 years ago, while emissions from industry have declined in the same period.

The European Union has committed to reducing its overall carbon dioxide emissions by at least 20 percent by 2020 and by half by 2050. To achieve those goals the region will have to curb auto emissions, most likely through changes in car design, fuel types, traffic control and driving habits.

"We believe that CO2 from personal transport has to be decreased in a holistic way, with contributions from all sectors — no one thing will bring levels down," said Ivan Hodac, secretary-general of the European Automobile Manufacturers' Association in Brussels. He said that if all sides cooperated, levels could come down 25 percent in the next five to seven years.

The industry is investing heavily in improving the fuel efficiency of conventional cars as well as in designing hybrids and vehicles powered by alternative fuels like electricity and hydrogen, Hodac said. But these design changes will take at least five years to come to market, and will not solve emissions problems on their own, he added.

"Everyone puts all the pressure on the manufacturers, and we're doing our part," he said. "But others should do their part as well; nothing much has been done with driving, improving infrastructure."

For individuals, lowering transport emissions can involve choosing more efficient vehicles, using public transportation or bicycles, driving at the most fuel-efficient speeds, and avoiding trips in congested areas. Several years ago, the Netherlands instituted a program to promote such behaviors, achieving a modest emissions reduction.

Recent studies have shown that rising fuel prices have to be combined with government intervention to force lasting changes in the transportation choices that people make.

Phil Goodwin, a professor of transportation policy at the University of West England, said research showed that a 10 percent increase in gas prices produced a 6 to 7 percent drop in fuel consumption over five years, because people drive less and switch to cars that are more fuel efficient.

"Price appears to be a highly effective way of influencing behavior," Goodwin said. "However," he added, "price alone doesn't win popular support or acquiescence. There has to be a package of a variety of different policies, including improvements to public transport, walking and cycling."

In studies performed for the British government last year, Ben Lane, a transportation consultant based in London, found a "very wide gap" between people's attitude toward the environment and their willingness to change their driving behavior.

The costs of buying and using a car are "weak but necessary" factors in pushing people to lower their transportation emissions, he said. More effective are laws that charge people for driving based on the estimated emissions of their vehicles.

Several years ago London instituted a hefty "congestion charge" for traditional vehicles entering the city center; hybrids and electric cars were exempt. Now, the London area has by far the greatest proportion of these alternative-fuel vehicles in the country, Lane said.

The resistance to changing driving behavior in part reflects practical problems in cities like Los Angeles and Rome, with poor public transportation. At a time of low fuel prices, people bought homes and accepted jobs in locations that required a car. Malls and offices are often built where land is cheap and there are few public transportation options.

Moreover, some people seem to have the same cost-is-no-object attitude toward cars that they have toward health. Valerio Roselli, 27, who works for Warner Brothers in Rome, continues to drive his SUV to work even though he could readily use public transportation. Rome's buses are hot, erratic and overcrowded, he said.

High fuel prices in Italy have forced many people to modify their habits, at least temporarily. Traffic dropped on the autostrada, a toll highway, by 2.5 percent between March and June. New car registrations are down 18.2 percent this year compared with last. Sales of Alfa Romeos have dropped by 27 percent. That may reflect the flailing economy here as well as high gas prices.

Some experts say it may take a few years to see whether Europe and the United States are nearing a tipping point for fuel prices that could affect where people live and how they get around.

"People cope for a while, and then it is not until the next time they move home or job or other such 'life-events' that a new travel pattern emerges," Goodwin said. "So the effect on new car sales, month by month, of changes in fuel price will be quite damped. This has led some people to think there is little or no effect, but that is probably wrong."