Everyone involved with Beijing's Olympic Games held their breath last week, not because of the city's famously polluted air, but in anticipation of the results of an experiment that could help to clean it up.

On Monday August 20, the last day of the four-day traffic easing test, they breathed a sigh of relief. The experiment, which saw 1.3 million vehicles taken off the city's roads, appeared to have been a success, easing worries about poor air quality during the Olympic Games next year.

The test may lessen the concerns of Jacques Rogge, President of International Olympic Committee, who told a CNN interview earlier in August that during the Beijing Olympics some endurance sports like cycling, where athletes have to compete for six hours, might be postponed or delayed to days when the air was cleaner. His remarks raised fears that Beijing's air would not be cleaned up in time for the event, despite strenuous efforts to make things better.

Over four days starting from Friday August 17, cars with even-numbered license plates were ordered off the roads Friday and Sunday, and vehicles with odd-numbered plates were banned on Saturday and Monday. Emergency vehicles, taxis, buses and other public-service vehicles were exempt.

Despite high temperatures and humidity, which slowed the dispersion of pollutants, the effects of the experiment were significant. Beijing had an air pollution index (API) of between 91 and 95 during the test days, according to the monitoring center of the city's environmental protection administration. The index hit 116 the day after the test and was 115 on August 16, the day before the trial began.

According to the Chinese scale of air quality, API between 51 and 100 indicates good air quality that will not affect outdoor activities while a reading of between 101 and 200 indicates slight pollution and people with heart and respiratory conditions are advised against outdoor activities.

"As the air quality during these four days reached the national standard, it was fit for all activities, including sports," said Du Shaozhong, Deputy Director of the Beijing Environmental Protection Bureau, speaking to a press conference the day after the test.

Du said the timing of the four-day drill was carefully selected to enable athletes to perform at their peak at the ongoing Olympic test events. August has a total of 12 international sports events under the "Good Luck Beijing" banner and six events took place during the traffic ban, including an international cycling road race tournament.

During the four days, access to public transport was increased across Beijing through additional buses and subway trains, and companies were encouraged to promote flexible work schedules, all measures adopted by previous Olympic host cities, including Atlanta and Athens. Most Beijing residents praised the traffic control experiment for easing traffic congestion. For PR account executive Lu Ying, her daily 50-minute trip from home on the northern third ring road to the office in downtown Beijing was shortened by a third.

Du said Beijing has taken more than 200 measures to clean up air pollution since 1998. As a result, before the opening of the Olympic Games, over 90 percent of the city's buses will meet Euro III Emissions Standards and Beijing already has nearly 4,000 natural gas-fueled buses, the largest fleet in one city in the world.