"When cars run at low speeds in traffic jams, they emit way more pollutants and usually consume more oil," said Hao Jiming, a member of Chinese Academy of Engineering.

Many people who had expressed annoyance over giving up their cars for blue skies are intensely scared of returning to days of choking smog and rush-hour congestion when the restrictions end after the Paralympics.

The Beijing traffic authorities have admitted receiving many submissions from car owners, saying they were comfortable with the odd-even number system and hoping it would last.

The city would continue to improve its public transport service by expanding transport networks while keeping fares low after the Olympics, said Zhou Zhengyu, deputy director of the Beijing Municipal Committee of Communications.

"We aim to create a more convenient and comfortable environment for people traveling in the city," he said.

The car ban might be a cure for congestions but not necessarily the best one, said Yang Kaizhong, an economist from Peking University.

He argued there were a variety of methods such as charging for causing congestion and raising parking fees which proved effective in some foreign countries.

WHAT'S AHEAD

For local government, challenges remained mainly in two aspects.

One was how to effectively restrict vehicles owned by governments and state companies, and develop shuttle bus schemes as alternatives. Some people had suggested to mark those "official" vehicles with distinctive signs to differentiate them from private cars.

The other was to maintain the prolonged subway service hours and increased trains and buses, and meanwhile continue building more roads.

For citizens, the biggest challenge could be the transformation of ideas. Driving a car would probably save one some time but it would cause many other problems that would do harm to the mass. People would eventually understand their individual interests were not in conflict with public ones.

Last but not least, the car owners would have to overcome the impulse to drive, which, some say, would be a test for them who were usually labeled China's "middle class".