Traffic flowed more smoothly but the sun was still shrouded by smog on Monday, the fourth and final day of Beijing's Olympic pollution prevention test.

To see if the city's poor air quality could be improved at least temporarily during next August's Games, the Chinese capital has taken up to 1.3 million cars off the roads by banning number plates ending in odd and even numbers on alternate days.

State media proclaimed the exercise a success, with the Xinhua news agency claiming late on Monday that the city had four "blue-sky days". But the skies -- and some athletes -- suggested a mixed verdict.

Seoul used similar traffic control measures when it hosted the Olympics in 1988, and Athens battled its pollution problem with the same tactics for more than a decade before it held the Games in 2004.

Pollution remains the main concern for organisers of the Beijing Games. Olympics chief Jacques Rogge said two weeks ago that some endurance events might have to be postponed if air quality was not up to scratch.

One such event is the 174-km (108-mile) cycling road race, and some of the world's top cyclists were in Beijing over the weekend for a test event.

Despite taking more than a third of Beijing's cars off the roads and a race course that took in the less polluted climes around the Great Wall, there were clearly respiratory issues for some competitors.

"I have a sore throat and lungs but unless we get everyone to stop driving for a month I guess there is not a lot we can do about it," Tour de France runner-up Cadel Evans told Australia's Sunday Telegraph after the road race.

Official air quality reports over the four days of car restrictions gave Grade 2 ratings on the National Scale of 1 to 5, with the major pollutant cited as large particulate matter. Grade 1 denotes "excellent" air quality and Grade 2 "fairly good".

UNFAVOURABLE

Beijing's Environmental Protection monitoring centre said the still, humid weather over the weekend had been unfavourable for "emission diffusion".

"The vehicle emissions such as nitrogen dioxide have been reduced continually over these days," monitoring centre Vice Director Zhao Yue told the bureau's official Web site (www.bjepb.gov.cn) on Sunday.

"If there had been no restrictions, the air quality would have worsened within one or two days but today it remained Grade 2. In this way the restriction showed an obvious effect on the air quality."

Some athletes and coaches, however, are concerned that China's pollution ratings do not take into account smaller particulate matter and ozone, both of which can have an adverse impact on the human body.

Beijing spent 120 billion yuan ($15.80 billion) from 1998 to 2006 on environmental improvement -- shutting down or moving the worst industrial polluters, taking old vehicles off the roads and extending the city's rail and subway network.

The number of people taking the city's subway was 200,000 more than the usual average on the four days, Xinhua reported. And the city doubled the number of traffic police on patrol to 6,000 to make sure drivers behaved.

Bicycles have been more in evidence on the streets over the four days of the test and Xinhua news agency reported on Monday that a Beijing company would make 50,000 bikes available to rent at 230 outlets around the city before the Olympics.

Joining the "pick-up and drop-off" rental scheme will cost 100 yuan ($13.17) a year, the same amount car owners were fined for driving with the wrong number plate over the last four days.

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