Since the emission of smoke from motor vehicles is a major source of air pollution, specific standards for the permissible limits for such emission have been prescribed in the Motor Vehicles Act 1988 and Central Motor Vehicles Rules 1989. All vehicles which are in operation for more than a year should undergo emission tests every six months. The Government has authorized 248 Private Emission Testing Centers throughout Tamil Nadu as per rule 116(B) of Tamil Nadu Motor Vehicles Rules 1989 and has made it mandatory that at the time of every transaction with Regional Transport Offices, certificate of Pollution Under Control will be checked.