Beijing plans to control the number of vehicles on the road, suspend some earthwork projects and ask polluting enterprises to cut back on production to ensure clean air for the 2008 Olympic Games, environment and transportation officials said yesterday.

They lauded a four-day traffic control trial which concluded on Monday as a success.

Vehicles with odd and even plate numbers took turns on the road from Friday to Monday; and people were encouraged not to travel in private cars to Beijing during the period.

Traffic authorities said that about 1.3 million cars, more than a third of the city's total, were off the road during the four days. Millions of car owners took cabs, buses and subways or rode bikes again.

The Beijing municipal government sent short messages to residents to thank them for their cooperation.

Du Shaozhong, deputy director of the Beijing municipal environment bureau, told a press conference yesterday that the city registered "four blue sky days" with Grade 2 air quality, only a notch below the best.

He said the air was suitable for outdoor sports like the marathon.

The air quality improved immediately after the traffic control exercise began, with emissions of air pollutants like carbon monoxide dropping 15 to 20 percent, he said.

Air quality relapsed to Grade 3 yesterday after the traffic controls were lifted.

"The trial proved to be successful as we collected valuable data to work out a valid plan to rein in pollutant emissions during the Games," the official said.

Liu Xiaoming, deputy director of the Beijing municipal committee of communications, said that the trial strengthened their confidence in improving public transportation to ease traffic jams.

The data collected will help officials decide on how many vehicles are to be allowed on the road during the Games, Liu said.

Du said that the city will also set limits on construction sites and heavily polluting factories.

A detailed plan to ensure air quality during the Games will be released by the end of this year, he said.

The Beijing environment protection bureau earlier announced that the city experienced 133 "blue sky days" - when air quality reaches Grade 2 - in the first seven months of this year, compared to the goal of 245 days for the whole year.

The city is home to more than 3 million vehicles, and the number is still increasing at about 1,000 a day.

(China Daily August 22, 2007)