Northern City Line

The Great Northern & City Railway (GN&CR) was planned to allow electrified trains to run from the Great Northern Railway (GNR, now the East Coast Main Line) at Finsbury Park to the City of London at Moorgate. Despite being built using similar methods to the tube network then under construction, the tunnels were built large enough to take a main-line train, with an internal diameter of 16 feet (4.9 m), compared with those of the Central London Railway with a diameter less than 12 feet (3.7 m). For this reason the line was popularly known as the "Big Tube" in its early days.[9] However, the GNR eventually opposed the scheme and cancelled its electrification plans, and the line opened in 1904 with the northern terminus in tunnels underneath Finsbury Park GNR station. It was originally electrified using an unusual fourth-rail system with a conductor rail outside both running rails.[10]

The GN&CR was bought in 1913 by the Metropolitan Railway (MR), which operated what are today the Metropolitan and Hammersmith & City lines and the former East London line. The MR had plans to link it to the Circle and Waterloo & City lines, but these were never fulfilled.[10] During this period, the line remained an isolated branch, without through services to any other part of the rail network. Carriages were brought to it through a connection into a freight yard near Drayton Park station, where a small depot was built to service trains.

The GN&CR generating station closed when the MR took over, and became the studio of Gainsborough Pictures. After lying derelict for many years, it became a temporary venue for the Almeida Theatre. It has since been redeveloped as apartments.

After the formation of the London Passenger Transport Board in 1933, the MR was amalgamated with the other Underground railways and the line was renamed the Northern City Line. In 1934 it was re-branded as part of the Edgware–Morden line (which was renamed the Northern line in 1937), and in 1939 operations were transferred from the Metropolitan to the Northern. As part of London Transport's New Works Programme, the Northern Heights plan was to connect the Northern City Line at Finsbury Park to existing main-line suburban branches running to Alexandra Palace, High Barnet and Edgware, which would be taken over by London Transport and electrified. The Highgate branch of the Edgware–Morden line would connect to this network north of Highgate. Only parts of this plan were completed: when the Second World War started, the Highgate link and electrification of the Barnet branch were well under way and ultimately completed, but the Northern City connection to Highgate was first postponed and finally cancelled after the war.

The planned 1930s Northern Heights extensions, showing the diversion of the Northern City Line to Alexandra Palace, Bushey Heath and High Barnet. Sections marked in solid green were ultimately taken over. The line from Highgate to Finsbury Park already existed but was to be absorbed by London Transport; this never happened and it closed to passengers in 1954. After being used to transfer tube trains from Highgate depot to the Northern City line, it closed permanently in 1970.

After the war there were proposals to extend the Northern City Line north and south. The London Plan Working Party Report of 1949 proposed several new lines and suburban electrification schemes for London, lettered from A to M. The lower-priority routes J and K would have seen the Northern City Line extended to Woolwich (Route J) and Crystal Palace (Route K), retaining the "Northern Heights" extensions to Edgware and Alexandra Palace. The lines would have run in small-diameter tube tunnels south from Moorgate to Bank and London Bridge.[11] The "K" branch would have run under Peckham to Peckham Rye, joining the old Crystal Palace (High Level) branch (which was still open in 1949) near Lordship Lane. Nothing came of these proposals, and the Edgware, Alexandra Palace and Crystal Palace (High Level) branches were all closed to passengers in 1954. As a result, the Northern City Line remained isolated from the rest of the network.

In 1964, the Northern City Line (low level) platforms at Finsbury Park were given over to become the southbound platforms of both the Piccadilly line and (then new) Victoria Line, the former Piccadilly line platforms becoming the northbound Piccadilly and Victoria lines' platforms. From this time the NCL used Drayton Park as its terminus. At the same time a change was made at Highbury & Islington, with the northbound Northern City line diverted to a new platform alongside the northbound Victoria line, and the southbound Victoria using the former northbound Northern City platform, both providing cross-platform interchange. Passengers from Moorgate to Finsbury Park took the Northern City line to Highbury & Islington and then changed onto the Victoria Line.

In 1970 the line was connected (as intended by its original promoters) to the mainline via the high level platforms at Finsbury Park as part of a wider plan to electrify ECML suburban services. The line was renamed Northern line (Highbury Branch) and the following year an agreement was made to transfer it to British Rail. Commuter trains were run to/from Moorgate instead of King's Cross, relieving congestion at King's Cross.

The last London Underground services ran in October 1975 and British Rail services commenced in August 1976, replacing services to Broad Street via the city branch of the North London Line. These British Rail services used the name "Great Northern Electrics". The track and tunnels are now owned by Network Rail. Services are provided by Great Northern to Welwyn Garden City and, via the Hertford Loop Line, to Hertford North (with some extending to Stevenage, Hitchin or Letchworth). The name "Northern City Line" has been revived to refer to the underground part of the route.

From Finsbury Park to Drayton Park traction current is supplied at 25 kV AC via overhead line, controlled by York Electrical Control Room.[12]

Network SouthEast branding at Essex Road station.

From Drayton Park to Moorgate traction current is supplied at 750 V DC via third rail. There are two electrical sections,[12] separated by a gap at Poole Street:

• Queensland Road to Poole Street
• Poole Street to Finsbury Circus

Trains change from AC to DC traction supply, or vice versa, whilst standing at Drayton Park station.[12] The platform starting signal on the Up platform at Drayton Park is held at danger (red) as the train approaches. This ensures that all trains stop to lower the pantograph before going into the tunnel.

In the 1970s the original London Underground fourth-rail traction current supply was converted to a third-rail 750V DC system. The redundant centre fourth-rail was disconnected and left in situ since it was difficult to remove in the narrow tunnels.[13]

Signalling is controlled from Kings Cross power box.[12] Between Drayton Park and Moorgate, there is no Automatic Warning System or Train Protection & Warning System equipment provided, due to the position of the auxiliary return rail.[12] All signals are multiple aspect colour light signals fitted with train stop arms.[12]

Works to commission new ETCS digital signalling on the line, along with the first test train under the new system, took place during the Early May Bank Holiday in 2022.[14] The new signalling system was approved by the Office of Rail and Road in March 2023, with passenger services expected to switch over to the new system by the end of 2023.[15]

NCL Start of Procedures sign & Up platform starting signal at Drayton Park

Because mainline trains operate over the infrastructure inherited from London Underground, there are some practices on the NCL which differ from Railway Rulebook instructions, and these are contained in an additional publication.[12] These include:

Class 313 unit at Moorgate

As part of its contract to supply electrical equipment during the construction of the line, in 1901 British Thomson-Houston provided 35 sets of traction control equipment to Brush Electrical Engineering Company and Dick, Kerr & Company. The original plan was for 11 seven-car trains (33 motors and 44 trailers) and one shunting locomotive. Initially 26 motorcars and 32 trailer cars were built. They were known as the 'wooden' cars because they were fabricated of teak and mahogany on steel underframes. In 1906 Brush delivered another five motors and 13 trailers. There were of all-steel construction and naturally-enough referred to as 'steel cars'. The GN&CR converted one trailer to a motor car, bringing the fleet to 32 motors and 44 trailers. (The remaining sets of traction control equipment were used as maintenance spares.) Normal operation was six-car formations at peak times, reduced to two-car sets at other times. Cars were 56 ft 6 in (17.22 m) long over buffers, 9 ft 4 in (2.84 m) wide, and 12 ft 2 in (3.71 m) in height. Seats were provided for 58 passengers in the wooden trailers and 64 in the steel ones. Motor cars seated 54 because of a 2 ft 10 in (86 cm) equipment compartment behind the driver's cab. Uniquely in England, coupling between cars was by means of link and pin on the centre-line.[16]

The original fleet of 76 carriages was withdrawn and replaced by London Underground Standard Stock on 15 May 1939.[16] These became the last pre-1938 trains running on the Underground, being phased out during the last weeks of October 1966 through 3 November. 1938 tube stock serviced the line, in variously three-, four- and six-car formations, until its temporary closure on 4 October 1975.[17]

Services are currently operated by dual-voltage Class 717 electric multiple units (EMUs), which replaced Class 313 units as part of a franchise commitment when Govia Thameslink Railway took over management of the line and its services.[18] The Class 717s began to enter service in March 2019.[19] To comply with regulations for trains operating in single-bore tunnels where there is not enough clearance space for side evacuation, they have emergency doors at both ends of a unit. When operating on 750 V DC, the two motor coaches of a Class 313 collected traction current from their own shoe gear only; there was no traction bus linking them together as found on most Electric Multiple Units. All of the Class 313 units when operating on the NCL had their Driving Motor B vehicle at the London end, and whilst on 750 V DC were electronically limited to 30 mph (48 km/h),[20] which is the maximum line speed.[4] All stations are long enough to accept six-car trains.[21]

This is the number of passengers using stations on the line from the year beginning April 2002 to the year beginning April 2019.

• Northern Heights plan

Wikimedia Commons has media related to Northern City Line.

• Underground Line Guide – Northern line – comprehensive history of the Northern line and its branches