The A533 Expressway bridge near Runcorn is being replaced for National Highways with a new crossing just a few metres away.
Preparations started in November and construction of the building site compound started last week.
Lead contractor AmeySRM is a joint venture of Amey and Sir Robert McAlpine.
The existing bridge was built in 1971 and is being replaced with a new 67-metre two-span concrete bridge, consisting of a single two-lane carriageway and a combined footpath and cycleway.
The old bridge will be demolished once the new one is ready. This presents challenges. Access will be restricted as it will be sandwiched between the new one and an existing West Coast main line railway bridge. Internet and water services are carried across the motorway by the existing bridge and have to be diverted.
The topography is also a challenge as the bridge is skew across the M56 and the land falls on the southern side of the motorway. This requires a complicated design for the bridge decks and concrete parapets in the motorway verges.