The Northern Line is one of the two lines owned and operated by Merseyrail on Merseyside, England, the other being the Wirral Line (Merseyrail's City Line is not owned or operated by Merseyrail). It connects the centre of Liverpool with Hunts Cross to the south and Southport, Ormskirk and Kirkby to the north. It crosses the centre of Liverpool by a tunnel built in the 1970s, known as the Link. The line is allocated the colour blue on maps of the Merseyrail system.
Brunswick station on the Southport - Hunts Cross section was added in 1998 to provide a connection to the Brunswick Business Park.
Trains from Hunts Cross continue to Southport, while trains to Ormskirk and Kirkby start from Liverpool Central. Trains operate every 15 minutes on each of the three routes (Monday to Saturday) and every 30 minutes on Sundays, except in the summer months when Sunday frequencies on the Southport - Hunts Cross route are increased. On the same route, the frequency is as little as every 8 minutes during peak hours. Trains on the Southport - Hunts Cross and Ormskirk - Liverpool Central routes are increased to 6 carriages during peak hours. Weekend services during the summer on the Southport route are 6 carriages all day.
The Northern Line is electrified using a 750V DC third rail. The line from Liverpool Exchange to Southport and on to Crossens and Meols Cop, was the first part to be electrified in 1904, followed by the branch to Aintree (on the Ormskirk branch) in 1906 and then on to Ormskirk in 1913. The Kirkby branch and the line south of Liverpool as far as Garston were electrified to coincide with the construction of the Link in 1978 and the electrification cut back to Southport in the north. The section from Garston to Hunts Cross was electrified in 1983, allowing services to be extended.
Interchange with the Wirral Line is available at Liverpool Central and Moorfields. As the Northern Line does not pass through Liverpool Lime Street (which is the city's main National Rail station), passengers must use the Wirral Line as a connection (although in practice, given the relatively short distance between Central and Lime Street, many prefer to walk).
Interchange with other National Rail services can be made at Southport, Ormskirk, Kirkby, Liverpool South Parkway and Hunts Cross.
This list is incomplete.