BEIJING — Half of Beijing's 3.3 million vehicles will be pulled off the roads during the Olympics to help clean the city's noxious air for the games.
The auto ban is part of an anti-pollution plan that also will halt construction and heavy industry during the Olympics, which begin in seven weeks.
Under the plan announced Friday, vehicles will be allowed on the roads on alternate days _ according to even or odd car registration numbers _ from July 20 until Sept. 20.
In addition, 300,000 heavy polluting vehicles _ aging industrial trucks, many of which operate only at night _ will be banned from July 1.
New sports venues and $40 billion spent to improve China's infrastructure have not disguised the fact that Beijing's air quality remains a contentious issue for the games.
International Olympic Committee president Jacques Rogge had said outdoor endurance events lasting more than an hour will be postponed if air quality is poor.
"Ironically, the one place where expectations are so low are on the environment, where China may come out looking better than people thought," Victor Cha, director of Asian Studies at Georgetown University, said in an e-mail.
"Pea-soup air at the opening ceremony would be their worst nightmare, however," Cha added.
The Beijing Olympics take place on Aug. 8-24, followed by the Paralympics Sept. 6-17. About 500,000 foreigners are expected for the games, with 10,000 athletes and about 30,000 journalists.
Beijing has long said it would limit the number of vehicles on roads for the Olympics, but Friday's announcement gave the most details yet, including the specific dates when the rules would take effect.
Under the plan, between 30 percent and 70 percent of 300,000 government-operated vehicles will be taken off the roads. Officials also expect a strong increase in the use of public transportation, with several new subway lines set to open. Several others have opened in the last year.
The traffic plan was announced on a day when Beijing sweltered under a thick haze of pollution, limiting visibility to a half-mile. Conditions were even worse Thursday, although the Beijing Environmental Protection Bureau's Web site described conditions for both days as only "slightly polluted."
"Perception is often different from the scientific monitoring statistics," said Du Shaozhong, deputy chief of Beijing Environmental Protection Bureau. "We base our findings on data.
"We now have 27 monitoring stations which all use state-of-the-art equipment," Du added.
Du had repeatedly denied charges that officials moved the monitors away from polluted areas to get better readings.
"We have the confidence and capacity to provide good air quality for the Beijing Olympics," Du said. He estimated that car emissions would be cut 63 percent by the ban and other measures.
The plan will also prohibit most vehicles entering the city from outside Beijing. These vehicles will need special permits and must meet air quality standards. Officials said violators would be punished under "applicable regulations," but gave no specific details about fines or other sanctions.
Officials said that 95 percent of the city's 66,000 taxis would be operating during the games, along with 21,000 buses.
A similar plan was tested for four days last summer, and the measures announced Friday were widely expected.
Five days after the July 20 ban goes into effect, special Olympic traffic lanes will begin operating and will stay in place until Sept. 25. The city will set aside 165 miles of roadway, where certified Olympic vehicles will be allowed to move from hotels, Olympic venues and the Athletes' Village. The average speed is expected to be 35 mph.
Setting aside special lanes is the only way to move traffic along Beijing's chaotic, crowded roads.
Officials have said that during the same two-month period, most construction in the city will halt, heavy industries will close, and even spray painting will stop to clean the air. Some reports suggested that production cutbacks could come even sooner.