John Sisk & Son has been appointed to carry out a £78m upgrade of Junction 10 of the M6, whose cost has risen from the initial £64m.
The contractor will design and build the new junction at Walsall, which will replace the bridges over the motorway.
Highways England said the scheme, which is a joint venture between itself and Walsall Council, supported by the Black Country Local Enterprise Partnership, will increase capacity at the traffic bottleneck and improve safety.
It said significant congestion at the junction and the surrounding area was identified as one of the main transport issues facing the region in the West Midlands Strategic Transport Plan.
The current junction is over 50 years old. Highways England said replacing the bridges that carry it over the motorway will avoid extensive maintenance while the new bridges will also make the junction larger.
Project manager David Reed said: ‘We are delighted to announce that John Sisk & Son have been appointed to lead this important scheme which will tackle congestion at a very busy junction at the heart of the country.
‘This is a significant milestone for the project which will ultimately bring smoother and safer journeys for the many thousands of drivers using Junction 10 every day.’
Although Highway’s England’s announcement gave the value of the upgrade as £78m, its webpage for the scheme cites a cost of £64.5m.
Mr Reed told Highways: 'The original scheme budget was based on market rates and conditions at the time in 2015. As we have developed the detailed design and carried out investigation surveys, we have found that the ground conditions require more work than anticipated.
'The revised cost reflects this requirement and also takes into account adjustments in line with current inflation levels.'
It said the new junction will facilitate growth at the Black Country Enterprise Zone in Darlaston and improve accessibility for cyclists and pedestrians.
Following a public inquiry in April, the transport secretary has confirmed the orders to acquire the land needed to alter the junction and layout of the local roads and motorway slip roads.
Highways England said only a small area of land is needed on a permanent basis as the scheme uses existing highway land where possible.
Paul Brown, managing director UK Civils, John Sisk & Son, said: ‘Sisk is delighted to be awarded this major highways scheme. The project provides us with an opportunity to further enhance our reputation and continue our excellent relationship with Highways England, following the recent successful completion of the A19 works in the North East.’
Preparation work is expected to get under way in the autumn with construction work beginning in January. Work is due to be completed by summer 2022.