First phase (completed)

The first part, which was completed within three years, was from Walton, Liverpool, to the junction with the A6 at Irlams o' th' Height in Salford. The 29.5-mile (47.5 km) road was constructed in an almost straight alignment with few curves.

To be a high-speed trunk route, its 1930s planners designed some parts to be three roads in one. The central section was exclusively for through traffic while adjacent side roads – either side of the main carriageway – provided local access.^[1] Although the sections within Liverpool were dual carriageway from the beginning, a few short stretches through Salford continue to use the original three-lane layout. The rest of the road was converted to dual with a central reservation in the 1950s and 1960s. Many of the original 1930s bridges remain; they were built from steel in preparation for any future expansion as they would be easier to replace than ones constructed from moulded concrete.

The road remains the UK's largest pre-motorway project. In 2004 the Highways Agency detrunked the road, passing control and maintenance over to the local authorities along its route.

Second phase (never developed)

With the completion of the first phase, the next stage was to extend the road beyond Salford and into East Lancashire proper. However this was never undertaken. Its failure was largely due to the road's location. Despite linking North West England's largest cities, the East Lancs remained isolated from the rest of the UK's national road network. Both ends of the highway began in high-density urban areas that were not close to any comparable infrastructure that could assist rapid transit connections.

By 1942, proposals were put forward to extend the A580 across the Pennines to Hull on the east coast of Britain.^[2] Although this plan never came to fruition, its purpose became the foundation for the construction of the M62 motorway in 1960.