TRaVELLERS on public transport can cause more damage to the environment than those using a limousine, according to government statistics.  a typical bus outside London emits 184.33g of carbon dioxide per kilometre per person if it carries the average load, 7.2 passengers.  a BMW 730d limousine emits 178g/km and can carry five people, The average car emits 138.4g/km but a Volkswagen Polo Bluemotion TDi supermini, emits 91g of carbon dioxide per kilometre - 22.75g/km per person if it is carrying four people.  The figures appear in a report from the Department for Environment, Food and Rural affairs and the Department of Energy and Climate Change.  In London, where public transport use is higher, buses still emit 85g/km for each of their average 16.6 passengers. They are, however, still greener than Hackney cabs, which emit 198g/km.  The coach is the greenest method of public transport with the average trip emitting 50g/km per person, ahead of national rail (53g/km), trams (71g/km) and the London Underground (73g/km).  Edmund King, the president of the aa, said: "There's a lot of misinformation about 'green' travel. It's time for a balanced, fact-based discussion on this issue."