The Calcutta High Court had given owners of commercial vehicles older than 15 years a one-year deadline that ended Saturday, but several transport groups have appealed the decision to India's Supreme Court, which is likely to hear the matter Tuesday.

"This is a green-letter day for the city. At last, it is being enforced," said Subhas Dutta, an environmental activist whose legal battle against the city's polluters brought about the court order last year.

According to government records, more than 60,000 vehicles, including three-wheeled autorickshaws, buses, taxis and trucks, will be phased out in the city of 15 million.

The government is also encouraging new autorickshaws and taxis to use compressed natural gas as fuel. All the phased-out vehicles used gasoline or diesel.

The air quality in Calcutta already had improved significantly Saturday, according to a survey conducted by Saviour and Friend of Environment, a private environmental group, and commissioned by The Times of India newspaper.

Readings in several busy areas of the city showed hydrocarbon levels had dropped by more than 50 percent while the oxygen content had gone up by more than 15 percent, according to SAFE.

While several residents welcomed the change, others worried about the lack of transport once the work week resumed Monday.

Arindam Chaterjee, a software company employee, said he had trouble finding a taxi Sunday.

"I wonder what the situation will be like on weekdays," he said.