BEIJING, Aug. 20 (Xinhua) -- Beijing's overall air quality improved during the four-day test period ahead of next August's Olympic Games in which more than a million cars each day were barred from the roads, according to the Beijing Environment Protection Monitoring Center.

    The test resulted in the removal of five million cars from roads in downtown Beijing and the air quality was classified as "fairly good" for the duration of the four days.

    "The index of inhalable particular matter (IPM), a major air pollutant, was 91, 93, 95, 95 over the past four days while it was116 on Thursday," said Zhao Yue, a senior engineer with the center.

    "The wind speed has been low in recent days, which was not conducive to dispersing the pollutants in the air," he said.

    An unhealthy haze still hung over the city throughout the weekend but Zhao said, "It should be affirmed that the ban of vehicles has improved the city's air quality."

    About one fifth of the total IPM in Beijing's air comes from vehicle emissions, according to Du Shaozhong, deputy director of Beijing Environmental Protection Bureau.

    The reduction in traffic congestion was the most obvious benefit of the program.

    Monday's traffic on almost all roads in downtown Beijing was even better than the first three days, said Shao Jie, an official with the transport department of the Beijing Public Security Bureau.

    "I have never seen smooth-flowing traffic in rush hour on Monday like this before," Shao said.

    Statistics from the municipal transport authorities showed the jammed road sections only accounted for 0.1 percent of the total roads on Monday, whereas on the previous four Mondays, the figure stood at 5.8 percent.

    More Beijing residents used the subway, buses or even bikes to travel to work. The city's subway system saw an increase of 200,000 passengers each day during the test.