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

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. <SEP> 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 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.  It is part of the Great Northern Route services and operates as the south-eastern branch of the East Coast Main Line (ECML). <SEP>  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. 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. <SEP> 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.