The central government is considering a tax on vehicle emissions in an attempt to tackle the pollution problem posed by the soaring number of private cars, mainland media reported. Zhang Yanyou, a deputy director of the capital's development and reform commission, was quoted by The Beijing News as saying research on the levy, part of an all-inclusive environment tariff, was under way. The ministries of finance and environmental protection were involved in the research, he said. Chen Sai, a researcher at the environmental watchdog, said a vehicle emissions tax might be needed to help the government promote lower carbon consumption, and balance economic development and environmental protection. 'There is no timetable yet as the research, which started two or three years ago, is at an early stage,' she said. The mainland became the world's largest vehicle market last year, surpassing the United States, with 13.6 million vehicles sold. Environmental authorities on the mainland say emissions from private cars are the main source of air pollution and pollution-related diseases in urban areas, affecting hundreds of millions of people.