In 1846, the Grand Junction Railway obtained an Act of Parliament authorising the construction of a bridge over the River Mersey at the Runcorn Gap.

The seven-year time limit passed without construction taking place and the powers granted by the act lapsed.

[12] The footway was closed to pedestrians in 1965 but remains intact for access by railway personnel and carries an 11 kV electrical cable between Widnes and Runcorn.

[9] Phase Two involved mechanical repairs and waterproofing the east and west bottom chords along all three spans.

[9] The bridge carries a double-tracked railway across the River Mersey; it has been recognised as a Grade II* listed structure.

The tracks are laid on a metal deck supported by top and bottom box-girder chords, carried on 8.5 metre-high trusses.

[9] The bridge superseded a centuries-old ferry and a pedestrian footbridge set alongside the main girders was provided on its eastern side.

[9] The approaches to the bridge on both sides accommodated its considerable height and a gradient of 1 in 114 was needed to obtain the necessary clearance beneath the central spans.

[9] The limited space, particularly on the narrow walkway, makes access difficult, sometimes requiring suspended scaffolding and climbing ropes.

More elaborate methods of moving supplies and equipment have included bespoke trolleys and lifting frames and helicopters.

[9] Work was carried on bridge's drains and waterproofing, especially the castellated turrets and the timber fenders that protect the piers from damage.

Work on the bridge requires authorisation from Halton Borough Council's planning authority and the Marine Management Organisation because of the potential impact on shipping.

It has been claimed that it was named after Ethelfleda, a ruler of the historic Anglo-Saxon kingdom of Mercia, and that the southern abutments and pier of the bridge have been built on the site of the Saxon burh that had been erected by her in 915.