Traffic on the capital's normally bustling roads was noticeably light, even for a weekend, under the new rules which ban cars with odd- and even-numbered licence plates from the roads on alternate days.

A drive in the morning yesterday from the south-west side of the city to a far north-eastern district, which normally takes more than an hour, required only half that time.

'It's great. It's like driving in the middle of the night,' attorney Fan Wenling said, as she left for the office.

The rules, in effect until the end of the Paralympic Games in mid-September, are part of a wider campaign to try to clear the air in Beijing, which is typically wrapped in acrid smog.

The largest source of pollution is believed to be the city's 3.3 million vehicles, whose ranks swell by an estimated 1,000 a day as increasingly affluent Beijing residents buy their own cars.

The government hopes to take 45per cent of the city's cars off the roads and reduce emissions by two-thirds.

Despite their efforts, however, a familiar light haze hung over the city of 17 million residents yesterday morning, illustrating the ongoing challenge Beijing faces.

Experts believe the pollution-curbing experiment may not work, as unpredictable winds could blow pollution into Beijing, despite factory shutdowns in the city and five surrounding provinces. Or, pollution could build up, as August is a month with, generally, little wind.

The new measures will not be truly tested until today, when the city's millions of commuters take to the roads under the new rules.

Businesses have been pressured to adjust their working hours to cut down on rush-hour gridlock. Also, most official cars have been impounded and almost all earth and cement works have now been closed.

Only cars with even-numbered licence plates were allowed on the streets yesterday, and motorcycle police could be seen at key intersections watching the traffic.

The authorities say violators will be caught by a network of 10,000 'smart' devices, including cameras and scanners.

Those caught will be fined 100 yuan (S$20) - a significant deterrent for many in China, where annual incomes remain far lower than those in developed countries, despite rising affluence

The restrictions do not apply to taxis. Some cab drivers welcomed the chance to make more money, while others worried about overwork.

'But it will be nice to drive in better road conditions for a while,' said cabbie Ma Guiwei.

AGENCE FRANCE-PRESSE, XINHUA, ASSOCIATED PRESS, REUTERS