Europe’s cities generally have stronger incentives to act. Built for the most part before the advent of cars, their narrow roads are poor at handling heavy traffic. Public transportation is generally better in Europe than in the United States, and gas often costs over $8 a gallon, contributing to driving costs that are two to three times greater per mile than in the United States, Dr. Schipper said.

What is more, European Union countries probably cannot meet a commitment under the Kyoto Protocol to reduce their carbon dioxide emissions unless they curb driving. The United States never ratified that pact.

Globally, emissions from transportation continue a relentless rise, with half of them coming from personal cars. Yet an important impulse behind Europe’s traffic reforms will be familiar to mayors in Los Angeles and Vienna alike: to make cities more inviting, with cleaner air and less traffic.

Michael Kodransky, global research manager at the Institute for Transportation and Development Policy in New York, which works with cities to reduce transport emissions, said that Europe was previously “on the same trajectory as the United States, with more people wanting to own more cars.” But in the past decade, there had been “a conscious shift in thinking, and firm policy,” he said. And it is having an effect.

After two decades of car ownership, Hans Von Matt, 52, who works in the insurance industry, sold his vehicle and now gets around Zurich by tram or bicycle, using a car-sharing service for trips out of the city. Carless households have increased from 40 to 45 percent in the last decade, and car owners use their vehicles less, city statistics show.

“There were big fights over whether to close this road or not — but now it is closed, and people got used to it,” he said, alighting from his bicycle on Limmatquai, a riverside pedestrian zone lined with cafes that used to be two lanes of gridlock. Each major road closing has to be approved in a referendum.