Costain and Vinci will deliver the £750 million M4 Corridor upgrade around Newport after being awarded the early contractor involvement deal.
Costain has a 50% stake in a three way joint venture with Vinci Construction Grands Projets and Taylor Woodrow.
Works include building 24km of new motorway and a 2.5km long cable-stayed viaduct crossing of the River Usk, as well as major remodelling of M4 junctions 23 and 29.
Scheme development work will commence immediately, leading up to an anticipated Public Local Inquiry in winter 2016/7. Upon successful completion of the statutory processes, the second stage of the ECI work, construction, could start in spring 2018.
Andrew Wyllie, chief executive of Costain, said: “We are delighted to be developing this critical infrastructure scheme for the Welsh Government.
“This award is further demonstration of the importance to Costain of long-term strategic partnerships with our customers, and our ability to deliver integrated consulting and project delivery services.”
The project forms part of the strategic roads network, and deliver government aims for a more efficient, safer and sustainable transport network, supporting and encouraging long-term prosperity in the region.