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.
A deadly earthquake last month and fierce human-rights protests on international legs of the Olympic torch relay have removed some of the scrutiny from Beijing's chronic air pollution. But sparkling venues and $40 billion spent to improve infrastructure have not disguised the fact that 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 Olympics with 10,000 athletes and about 30,000 journalists set to attend.
Under the temporary plan announced Friday, between 30 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 on Thursday, although both days the Beijing Environmental Protection Bureau's Web site described conditions 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.