The tunnels on an underground railway are easy to overlook. To passengers, they are just black holes that their trains emerge from, stop at the platform, then disappear into the tunnel portal at the other end of the platform.
But they are part of the live railway, so the track needs to be maintained and rails replaced from time to time. Some contain signalling, or turnouts, and they need maintenance too. Then there are the power and communications cables that run through them, radio feeds so the control centre can keep in touch with train drivers, emergency exits in case a train stops in a tunnel, works access points and lighting.
The tunnels themselves need inspection, in case the lining starts to deteriorate, or leak. And if it leaks, there is drainage to consider.
Then there is dirt, dust and litter. This gets sucked off platforms by the ‘wind’ of passing trains and deposited in the tunnel. Dirt falls off trains, and dust is generated from brake blocks. If too much dirt builds up, it can be a fire hazard, ready to be lit by sparks from the electrical power supply to the trains.
Not all tunnels have all of these problems, but they all need regular inspection – and cleaning.
The Northern City line is no exception. It runs from Moorgate station to Finsbury Park, and is in tunnel until just south of Drayton Park. London-bound trains stop at Drayton Park, lower their pantographs from the 25kV AC overhead supply, and deploy pickup shoes for the 750V DC third-rail system use in the tunnels.
Network Rail has just completed a six-month programme of track renewal, station redecoration and intense cleaning through the Northern City Line tunnels and stations, working with Govia Thameslink Railway (GTR), which operates Great Northern train services between Hertfordshire and Moorgate. Great Northern’s late evening and weekend services through the tunnels were diverted to King’s Cross while the work was in progress, so as to allow Network Rail’s engineers time to complete the work.
The programme started in 2019 when Moorgate station itself was spruced up with new tiling and better lighting. From December, the programme moved on, through the tunnels and the other three underground stations on the route – Old Street, Essex Road and Highbury & Islington.
The track and tunnel work will make services more reliable, reduce noise and vibration from the railway and improve the condition of the tunnels for both passengers and railway workers. The improvements at the stations, and a new £240 million fleet of Class 717 trains introduced last October, have transformed the environment for passengers.
Using specialist machinery, Network Rail has cleaned almost 17 kilometres (10.5 miles) of tunnels, renewed over 3.4 kilometres (2.1 miles) of 40-year-old track and replaced more than 1km of the ballast.
Essex Road’s platform walls have been treated to the same comprehensive retiling as Moorgate. GTR’s contractors stripped away about 40 tonnes of old tiles – over 4,000 sacks of rubble – and covered an area of some 600 square metres with bright new white and blue ceramics.
At Old Street and Highbury & Islington, damaged and drab tiling has been removed or repaired, with walls resurfaced in readiness for future decoration.
At all four stations, Network Rail has replaced the old light fittings with new LED lighting, and GTR gave the stations an extensive deep-clean over three weekends.
Paul Rutter, route director for Network Rail’s East Coast route, said: “Over the last year, Network Rail has carried out significant work to clean the tunnels on the Northern City line and to upgrade the track along the route.
“This work will improve the reliability of services, as well as making the area more pleasant for passengers and workers who use these stations.
“This project, coupled with the work which Great Northern have done, will vastly improve passenger experience and we look forward to them reaping the benefits.”
Tom Moran, managing director for Thameslink and Great Northern, said: “Weekend and late-evening services in and out of Moorgate are back up and running, which will help key workers and others for whom travel by train is absolutely essential.
“Our passengers are already enjoying our new air-conditioned trains, which last year replaced the UK’s oldest electric mainline rolling stock with a modern, fit-for-purpose fleet. Now, they will also see brighter, cleaner stations on the Northern City Line between Finsbury Park and Moorgate.”
Over the next few years, Network Rail plans to upgrade the signalling system in the tunnels to a modern, reliable digital system. Further work will mainly be done at night without affecting passenger services.