It will take up to six years for KMB to phase out its old diesel buses and three years to upgrade the rest of its fleet to be close to the latest EU emission standards, the city's largest bus operator said yesterday. KMB principal engineer Kane Shum Yuet-hung said all buses being phased out would be replaced with those that met the European Union's latest Euro IV emission standards. The company's fleet of more than 4,000 buses includes about 550 pre-Euro buses that have been upgraded to Euro I by installing catalytic converters. Reviewing KMB's performance on pollution control, Mr Shum said the firm needed two years to come up with a replacement plan for the oldest buses, plus an estimated three to four years to replace them. A double-decker typically has a lifespan of about 17 years. However, green activists said progress was too slow and the phasing-out of polluting buses should be completed in three years from now. 'By maximising the life cycle of the buses, KMB is forcing the public to breathe in foul air for another six years,' said Friends of the Earth acting director Edwin Lau Che-feng. He urged KMB to use the upgraded buses to run on routes previously run by the dirtiest vehicles. Tour groups using the new Lok Ma Chau border checkpoint would find it inconvenient if direct bus services did not serve the crossing, lawmakers said yesterday. Members of the Legislative Council's transport panel condemned the government's decision to bar cross-boundary coaches from the checkpoint, saying it limited passenger choice and would result in unfair competition. Deputy Secretary for Environment, Transport and Works Annie Choi Suk-han said environmental conditions did not permit an expansion of transport facilities at the crossing. Non-franchised buses will still be able to use the existing Lok Ma Chau crossing when the new checkpoint opens in July.