Question: What is the former name of the rail service to which the Northern City Line belongs?

Context paragraphs:
Airport Rail Link (Bangkok): The Airport Rail Link (ARL) (Thai: รถไฟฟ้าเชื่อมท่าอากาศยานสุวรรณภูมิ ) is an express and commuter rail in Bangkok, Thailand.  The line provides an airport rail link from Suvarnabhumi Airport, via Makkasan Station, to Phaya Thai station in central Bangkok.  Most of the line is on a viaduct over the main eastern railway.  It is owned by State Railway of Thailand (SRT) and operated by SRT subsidiary SRT Electrified Train (SRTET).  The 28.6 km Airport Rail Link opened for service on 23 August 2010.  Services originally consisted of both express services and the City Line, a commuter rail service with eight stations.  As of September 2014, all express services were suspended until further notice due to a shortage of rolling stock availability.

Highbury &amp; Islington station: Highbury & Islington is a London Underground and National Rail interchange station in the London Borough of Islington, north London.  It is served by the London Underground's Victoria line, London Overground's East and North London Lines, and Great Northern's Northern City Line.

Drayton Park railway station: Drayton Park railway station is a National Rail station in Highbury, in the London Borough of Islington.  It is on the Northern City Line between Highbury & Islington and Finsbury Park stations, 2 mi down-line from ; it is in Travelcard Zone 2.

Essex Road railway station: Essex Road railway station is a National Rail station in Canonbury in the London Borough of Islington.  It is on the Northern City Line between Old Street and Highbury & Islington , 1 mi down-line from , and is in Travelcard Zone 2.  The station is at the junction of Essex Road, Canonbury Road and New North Road, with the present entrance on Canonbury Road.  Operated by Great Northern, it is the only deep level underground station in London served solely by National Rail trains.  Between 1933 and 1975 the station was operated as part of the London Underground, as a short branch of the Northern line.  Between 1922 and 1948 the station name was Canonbury & Essex Road.  The name reverted to the original form in 1948.

Northern City Line: The Northern City Line is a branch railway and commuter line in England, which runs from Moorgate to Finsbury Park in London with services running beyond.  It is part of the Great Northern Route services and operates as the south-eastern branch of the East Coast Main Line (ECML).  It is underground from Moorgate to Drayton Park in Highbury from which point it runs in a cutting until joining the ECML south of Finsbury Park.  Its stations span northern inner districts of Greater London southwards to the City of London, the UK's main financial centre.  Since December 2015 the service timetable has been extended to run into the late evenings and at weekends, meeting a new franchise commitment for a minimum of 6 trains per hour until 23:59 on weekdays and 4 trains per hour at weekends.

Great Northern Route: The Great Northern Route (formerly known as Great Northern Electrics) is the name given to suburban rail services run on the southern end of Britain's East Coast Main Line and its associated branches.  Services operate to or from London King's Cross and Moorgate in London.  Destinations include Hertford North , Welwyn Garden City , Stevenage , Peterborough , Cambridge and King's Lynn .  Services run through parts of Greater London, Hertfordshire, Bedfordshire, Cambridgeshire and Norfolk.

Atlantic City Line: The Atlantic City Line (ACL) is a rail line operated by New Jersey Transit (NJT) in the United States between Philadelphia, Pennsylvania and Atlantic City, New Jersey, operating along the corridor of the White Horse Pike.  It runs over trackage that was controlled by both the Pennsylvania Railroad (PRR) and the Pennsylvania-Reading Seashore Lines.  It shares trackage with SEPTA and Amtrak on the Northeast Corridor (NEC) until it crosses the Delaware River on its own Delair Bridge into New Jersey.  The Atlantic City Line also shares the right-of-way with the PATCO Speedline between Haddonfield and Lindenwold, New Jersey.  There are 14 departures each day in each direction.  Conrail also uses short sections of the line for freight movements (which are segregated), including the NEC-Delair Bridge section to its main freight yard in Camden, New Jersey.  Unlike all other NJT railway lines, the Atlantic City line does not have traditional rush hour service.  The Atlantic City line is colored dark blue on New Jersey Transit's system maps, and the line's symbol is a lighthouse.

Hertford Loop Line: The Hertford Line (also known colloquially as the Hertford Loop) is a branch of the East Coast Main Line, part of the Northern City Line commuter route to London for Hertford and other Hertfordshire towns and an occasional diversion route for the main line.  The line is part of the Network Rail Strategic Route 8, SRS 08.03 and is classified as a London and South East Commuter line.

Target Field (Metro Transit station): Target Field Station (formerly known during construction under the names of Minneapolis Intermodal Station, Downtown Minneapolis Ballpark Station and The Interchange) is a multimodal commuter train and light rail station in Minneapolis, Minnesota.  Located in the North Loop area of Downtown Minneapolis, the station's name reflects the Minnesota Twins Target Field baseball stadium next to the station, Target Field.  METRO Blue Line light rail service started November 14, 2009; Northstar Line commuter rail service started November 16, 2009; METRO Green Line light rail service started on June 14, 2014.

Rail replacement bus service: A rail replacement bus service uses buses to replace a passenger train service either on a temporary or permanent basis.  The train service that is replaced may be of any type such as light rail, tram, streetcar, commuter rail, regional rail or heavy rail, intercity passenger service.  The rail service may be replaced if the line is closed due to rail maintenance, a breakdown of a train, a rail accident, strike action, or if the rail service is not economically viable.

Supporting paragraphs: Northern City Line Great Northern Route
Answer: Great Northern Electrics