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."