Three firms have been awarded the contract to start work on the £1bn M4 relief road project around Newport.
Construction firm Costain has been jointly awarded the contract by the Welsh government, alongside Vinci Construction and Taylor Woodrow.
The plans include 24km of new motorway and a 2.5km long viaduct crossing the River Usk, as well as major remodelling of M4 junctions 23 and 29.
Development work starts immediately.
Government officials said the initial work was the first 'Early Contractor Involvement' contract, to examine development and environmental surveys as part of the statutory work that must take place before construction.
The work will also assist an anticipated public inquiry into the relief road.
Andrew Wyllie, chief executive of Costain, said: "We are delighted to be developing this critical infrastructure scheme for the Welsh government."
However, the new road is already subject to a legal challenge, with a decision over whether a judicial review can go ahead expected on Thursday.