Streets filled up with cars have maintained a headache for metropolises all over the world.

But now, the idea of car-sharing displayed at the ongoing World Expo in Shanghai may help cities relieve this headache, reduce air and noise pollution and save parking space.

Proponents of the practice, originated from Bremen, a Hanseatic city in northwest Germany, believe that city-dwellers may not have to own cars all to themselves for better life quality.

"Many people don't always drive their cars," said Ulrik Hovelmann, curator of Bremen exhibition stand in the Urban Best Practice Area at the Shanghai Expo.

"In Bremen, most cars run only one hour daily but are parked for the left 23 hours," he said, adding that if careful arrangement could be made, more people can share one car.

A company named Cambio was founded in Bremen to make such arrangement.

According to a video clip played at the Bremen stand, a customer can book a car through phone or the Internet, and will then receive a PIN code, with which the customer can open a case at the nearest car-sharing parking lot, and get the key to the booked car.

"With more than 40 urban car-sharing stations, Bremen has around 1,000 fewer cars than it would without this idea," Hovelmann said.

More than 5,500 citizens are now sharing 150 cars with a base cost of 3 euros (3.75 U.S. dollars) per month plus actual mileage fee. In comparison, owning a private car may cost at least 400 euros (500 dollars) monthly in Bremen.

There are many advantages of car-sharing besides cost margin. "You don't have to care for parking, car washing, maintaining, tire changing, and many other troubles," he said.

For a city, the car-sharing model may also point to a way of low-carbon, environment-friendly, sustainable development, scientists say.

A report by ManagEnergy, a European Commission-sponsored research initiative on energy efficiency and renewable energies, called car-sharing "a key element to make cities a good place to live in."

The practice of Bremen reduces the number of cars, reduces the mileage driven by car, increases the use of public transport and improves the environmental quality, the paper said.

"Each car-sharing vehicle replaces 4 to 10 private cars," said German researchers. "Car-sharing in Bremen is calculated in a life-cycle analysis to have a reduction of CO2 (carbon dioxide) emissions actually of about 1,900 tons per year."

The calculation does not yet include further indirect positive impacts, such as downsizing in the type of cars or the reduction in the field of car infrastructure.

Staff at the Bremen exhibition stand told Xinhua that the car-sharing model was spreading fast in Europe.

Cambio reported a 22-percent revenue growth and 20-percent growth in customer number in 2009. In addition to nearly 23,000 customers in Germany, the company's scheme has been expanded to 17 cities in Belgium.

As the pioneer of car-sharing, the city of Bremen sees the ongoing Shanghai Expo as a best chance to promote its idea and share its experience worldwide, echoing the slogan of the Bremen exhibition stand -- "Sharing a vision."

For people in such densely populated Asian cities as Shanghai and Beijing, car-sharing may prove a more attractive solution than buying large amount of private cars, staff members at the Bremen stand said.

"If Shanghai, with a population of almost 20 million, had a car- sharing rate like Bremen's, around 20,000 fewer cars would drive around the Chinese city," said a brochure distributed at the Bremen stand.