This week two construction groups will win the job to build Crossrail, the £16 billion rail scheme that is designed to relieve crowding on public transport in central London.

The choice of the winners from an international field of bidders is expected to be made at a meeting of the Transport for London finance committee on Tuesday, with a public announcement the next day.

Construction industry sources say two American-led groups are regarded as slight favourites. Bechtel is expected to take the job of “project delivery partner”, which will see it take charge of the building of the central London section of the line. This will involve digging two large, deep tunnels from Paddington to east of Liverpool Street.

The other role, programme partner, will involve the overall management of the project. Legacy 3, a joint venture between the American group Parsons Brinckerhoff and Britain’s Balfour Beatty is tipped as favourite.

The sources said, however, that there was no certainty the two groups would take the top roles.

In the project competition, Bechtel is vying with Legacy 3, a joint venture between Laing O’Rourke and Atkins, and another led by Capita Symonds.

Bechtel is also in the running for the programme-partner role