The major engineering works required to integrate the Northern and Wirral lines became known as the 'Loop' and 'Link' Project. The main works were undertaken between 1972 and 1977. A further project, known as the Edge Hill Spur, would have integrated the City Lines into the city centre underground network. This would have meshed the eastern section of the city into the core underground electric city centre section of the network, releasing platforms at mainline Lime Street station for mid to long haul routes.

 

The Loop Line is a single track loop tunnel under Liverpool's city centre serving the Wirral lines. It was built to allow both greater capacity and a wider choice of destinations for Wirral Line users, which included the business and shopping districts of Liverpool city centre and Lime Street Station, Trains from Wirral arriving via the original Mersey Railway tunnel enter the loop beneath Mann Island and continue in a clockwise direction through James Street, Moorfields, Lime Street and Central, and return to the Wirral via James Street station. Part of the Loop line links to the Mersey railway tunnel built in 1886 from a disused siding near James street station that was originally going to be a branch to Huskisson Dock. At Lime Street and Moorfields new building work took place with all new platforms, only 1 platform at James street is new the other platform is the original 1886 platform and the link line at Liverpool Central uses the original 1892 platforms while the loop line below uses the new 1977 platforms.

 

The Link Line is a double track tunnel that links the Hunts Cross branch to the south with the Southport, Ormskirk and Kirkby branches to the north, thereby creating one line, the Northern Line. It provides direct access from the north and south of Liverpool to the shopping and business districts in the city centre via two underground stations, Liverpool Central and Moorfields, both of which also interchange with the Loop Line. The Northern Line effectively creates a north-south crossrail enabling passengers to travel from the south to the north of the city, and vice versa, via Liverpool city centre.

The present Northern Line underground station at Liverpool Central Low Level was originally the Mersey Railway terminus. A section of the original 1880s tunnel between James Street and Central stations was used to form the Link Tunnel. The remainder, between Paradise Street Junction and Derby Square Junction, was retained for use as a stock interchange line between the Northern and Wirral lines and also for a reversing siding for Wirral Line trains terminating at James Street when the Loop Tunnel is inoperative. The stock interchange section of the tunnel is not used for passenger traffic.

The Link Tunnel was originally intended to link the urban lines north and south of the city creating a north-south crossrail and an additional function in completing the western section of a planned double-track electrified suburban orbital line, circling the city's outer suburbs, known as the 'Outer Rail Loop'. However, the eastern section of the Outer Loop was never built due to budget cuts.

 

To the south of Liverpool Central Low Level Station, a new track layout was constructed as part of the Link Line project. This layout permitted the former Mersey Railway route to be connected to the former Cheshire Lines Committee route from the closed Central High Level Station and so allow the Northern Line to be extended in a southerly direction to Garston and, later, Hunts Cross. It was accomplished by excavating the trackbed of the high-level tunnel to connect the two routes by means of a gradient. As it was still necessary to accommodate a reversing siding to serve Central Low Level, and as the width of the high-level tunnel did not permit a three-track alignment, a new section of single-track tunnel was built for the Central to Garston line. This tunnel starts to the south of the station and rises to join the high-level tunnel.

At the time of construction, the opportunity was taken to construct two short header tunnels for the proposed Edge Hill Spur project. Should the project go ahead, the connecting tunnels could be constructed without the need to obstruct rail services on the existing route. The junction arrangement would be a burrowing junction, as at Hamilton Square , with the grade separation of tracks increasing capacity.

 

The loop line was closed for most of 2017 as it had been 40 years since the track had been laid back in 1977, this will not need to be done again till the year 2077.

 

Passanger Stations Along Link & Loop Lines