SHANGHAI, Aug. 17 -- BEIJING'S traffic control test for next year's Olympics was said to have gone well on the first day of its four-day trial as hundreds of thousands of private cars were pulled off the capital's streets.

Beijing announced last week that it would use an odd-even license plate number system from August 17 to 20 to improve the city's air quality during test events for next year's Olympics. Only vehicles with license plates ending in odd numbers are allowed on the roads today.

An estimated 400,000 private cars were affected by the control today. It made Beijing's traffic flow much smoother than usual, the Beijing-based Qianlong.com reported.

Traffic authorities use electronic facilities to catch any one who has violated the ban. They will be fined 100 yuan (US$13) if caught driving in the city and ordered to return home, the report said.

Violators will be fined another 100 yuan if they refuse to return home, it added.

Most drivers complied with the odd-even license plate traffic control today.

"We should strongly support the control as it is for the Olympics," the report cited a person called "Tianyilao" as saying on Huilonguan BBS, a large community Website in Beijing. "And we can opt to car pool to save money and if the option goes well, we can continue do it in the future."

Other commuters also choose to take taxis, buses, or subways to work or simply take the day.

Emergency vehicles, taxis, buses and other public-service vehicles are exempt as are those given special passes by Beijing Olympic organizers to attend sports test-events around the city.

Bus companies promised to run 700 to 800 more buses during the testing period and Metro lines will extend operation times. The traffic authority also said more than 95 percent of the 66,000 taxis in town will be available.

More than 200,000 private car-owners have promised that they will not drive cars during the period and the number is still on rise, the report said

Exhaust discharged by vehicles is a major source of pollution in the capital. A city with a population of about 16 million, Beijing now has more than three million vehicles and more than four million drivers.

During the China-Africa Cooperation Forum nine months ago, up to 40 percent of residents used public transportation and about 800,000 vehicles were off the streets, which improved traffic and air quality during the six-day meeting.