Ministers also plugged gas-powered vehicles as a way of tackling pollution and congestion in Britain's choking cities.
The country's first motorway bus lane will, the Government hopes, provide a cheap, quick alternative to cars for passengers travelling from central London to Heathrow Airport.
The route will run along the southbound spur of the M4, between junctions 4 and 4A beyond Heston, with a car-free lane separated from the rest of the motorway by a small wall.
The 1.5km lane, being funded by the airport at a cost of pounds 1m, is expected to cut at least 15 minutes off the bus journey time, which normally takes about 75 minutes. At its peak, the new bus lane will carry 37,000 bus and coach passengers per day.
Announcing the extension,Glenda Jackson, the transport minister, said work was expected to start in July and will be completed by mid-autumn.
"I hope this will be the first of many schemes to make life easier for travellers, as well as helping to reduce road congestion," she said.
The completion of the new bus lane will coincide with the launch of FastTrain, a new 30-minute rail link between Paddington station in London and Heathrow Airport.
Mike Roberts, Heathrow's managing director, said: "Our vision is to have 50 per cent of passengers travelling to the airport by public transport and to help us achieve this goal we are investing over half a billion pounds in practical and workable public transport alternatives to the car."
Ms Jackson also called for industry to take up a new liquid gas-powered bus. She said it was an "attractive, greener" alternative to the car. "Tackling urban congestion is perhaps our most important challenge."
"Cleaner, greener buses have a key part to play in changing attitudes and making public transport a more attractive alternative to the private car," she added.
Shell UK, Daf trucks and the Energy Saving Trust demonstrated the new greener bus, which is similar to ones used in Holland and Denmark.
It is claimed they reduce exhaust emissions and noise compared with normal diesel engines. Fuel costs are similar to diesel.Reuse content