There was hardly a car to be seen on downtown Sao Paolo's usually snarled roads on Wednesday as 200,000 motorists stayed away for a pollution alert drill.

Motorists were given two days' notice of the drill as they would in case a real state of alert was declared.Cars are believed responsible for 90 percent of the air pollution in Sao Paulo, Brazil's largest city with more than 16 million residents. In a state of alert they would be banned from the roads until pollution fell to acceptable levels.

The state pollution watchdog, Cetesb, and the enviornment secretary declared the drill a success.

"It's splendid. Most of the population has adhered to our request. Hardly any cars can be seen," Environment Secretary Jorge Wilheim told reporters at one downtown viaduct.