Contracting giant Costain has won a three-year contract worth £85m to upgrade the Bidston Moss Viaduct in Wirral.
Design work will begin this month and last for about 15 months. Construction will start in summer 2010 and take around 20 months to complete.
The scheme will involve major strengthening work to the existing viaduct at Junction 1 and will allow the removal of current vehicle weight restrictions, which limit HGVs to using the inside lane only and impose a 3.5-tonne limit on the outside lane.
The Highways Agency, Wirral council and Merseytravel are working together to develop the scheme.