SHANGHAI, Aug 18 -- AIR quality improved slightly yesterday as Beijing began a four-day experiment to test whether pulling 1.3 million cars off the capital's roads each day would be effective in reducing air pollution during the Olympics next year.

Drivers with even-numbered license plates, excluding taxis, buses and emergency vehicles, were told to stay off the roads yesterday or face 100-yuan (US$13) fines.

Odd-numbered cars will be banned today and Monday, while vehicles with even-numbered registrations must also stay at home tomorrow.

"The experience we gain from this test will shed light on the adoption of measures to guarantee environmental quality at the Olympic Games next year," said Du Shaozhong, deputy director of the Municipal Environmental Protection Bureau.

The test period will also determine whether public transport can cope with the higher number of passengers and its effect on easing congestion, said an official with the Municipal Transport Commission.

Experts said pulling 1.3 million motor vehicles off the roads in Beijing each day can reduce exhaust emissions by 40 percent.

The air quality index yesterday registered 91. Readings between 51 and 100 represent "fairly good" air quality. The figure on Thursday was 115, classified as "slightly polluted."

But an unhealthy haze still hung over the capital yesterday despite the traffic restrictions.

Guo Hu, head of the Beijing Meteorological Observatory, said the weather conditions in the city, which is surrounded by mountains on three sides, make it difficult for pollutants to dissipate. Guo expected conditions to remain stable for the next few days due to a lack of significant cold air currents or rainfall.

Traffic flow appeared to be lighter on the first day of the test. There were fewer motor vehicles on the roads during the morning rush hour, and office workers who took shuttle buses to work said they arrived at their jobs much earlier than usual.

A man surnamed Xu, who lives in the outlying Daxing District and owns a Honda with an even-numbered registration, usually drives to his office in downtown Beijing.

He had to leave his car at home yesterday morning and take a shuttle bus arranged by his residential compound to Fuxingmen, about a 15-minute walk from his office.

"It was a pleasant experience as I had a chance to relax and get some exercise by not driving," Xu said.

A spokesman for the Beijing Public Transport Holdings Ltd said the usually clogged city roads were much clearer yesterday, lifting the efficiency of public buses.

The number of buses has been increased and running times extended by an hour during the test period.

Around 1,600 taxis will be allocated to train stations and airports each day, and more than 300 taxis will stay at more than 10 venues of the "Good Luck Beijing" Olympic test event, according to the transport commission.

Officials estimated that 8.4 million people will take public transport, including buses, the subway and taxis, over the four days, compared with 6.4 million on average.

(Xinhua/Shanghai Daily)