The new Routemaster should be in service by 2011
Bus manufacturers have been invited to submit their plans for London's new Routemaster buses.
The city's mayor, Boris Johnson, announced the new design in December following the New Bus for London competition.
Manufacturing firms are now being asked to show Transport for London (TfL) how they would combine their engineering solutions with the winning designs.
The first buses are expected to be in service by 2011.
"A number of great ideas were harvested from the New Bus for London competition," said TfL's David Brown.
"We are now taking those ideas to the bus manufacturers for them to come up with a final design for our new bus, and we're well on track to see the first of these on the road in 2011."
The new buses will be based on the joint winners' entries - the first by Aston Martin and architects Foster and Partners, and the second by Capoco Design.
The final design will have to meet all London bus requirements for vehicles in public service in London, including high standards of accessibility, safety, and emissions abatement.
The original Routemasters were phased out of regular service by the end of 2005 as they were inaccessible to wheelchairs or pushchairs.