The East London line, re-opened in recent times as part of the London Overground network, has an interesting history. To go under the Thames, it utilises the original Marc Brunel pedestrian tunnel.

Construction of the Thames Tunnel started in 1825, with son Isambard in charge of the ground works. After various technological problems that caused water to break in (which on one occasion nearly killed young Isambard) and financial difficulties, it finally opened in 1843 as a pedestrian tunnel amid much public interest. Anticipating that horse drawn carriages would use the tunnel, it was built with generous headroom, which was to prove fortuitous.

The novelty of walking through a dark tunnel in a not-too-salubrious district of London soon wore off, and the twin tunnels were converted for rail use in 1865. By building north and south cut-and-cover tunnel sections, an underground railway was created. So began the East London line, offering a service from the New Cross area to Wapping, Whitechapel, Shoreditch and, at one time, Liverpool Street, which eventually became a branch of London Underground’s Metropolitan line.

Brunel’s construction was so robust that it was not until 1995 that the Thames Tunnel, which had required only minimum maintenance down the years, was closed for urgent repairs, reopening in 1998.

The growing ambition of recent London Mayors to improve transport links led to the vision of creating an ‘outer circle’ route, of which the East London line would form part. This required main line signalling systems, so the line was again closed in 2007 for the conversion work. It is now busier than ever and carries services from West Croydon, Crystal Palace and Clapham Junction through to Dalston and Highbury & Islington.

Safety systems

As indicated previously, the Thames Tunnel is, in fact, two separate bores, although the underground extensions north and south are normal double-track brick-lined tunnels.

The UK rules for electrified underground railways require a system to be provided that enables the train driver to communicate with the signalling control room and for the driver to get the electric current switched off in an emergency. In addition, tunnel telephones are provided at stations and any sub surface equipment rooms that enable quick access to the signaller should a problem occur.

The technical solution for this requirement is well known and has been established practice for many years. It consists of two exposed copper wires running the length of the route at the height of a driver’s cab, mounted on ceramic insulators at periodic intervals that are bolted to the tunnel wall.

Drivers are provided with a portable telephone including a length of connecting cable and two crocodile clips. Once the train is stopped, the driver clips the telephone to the copper wires and a call is automatically initiated to the control room. At the same time, traction power is cut off as a signal is sent to the substation.

Pinching the two wires together creates a short circuit that also removes the traction power – an arrangement that is well proven and is familiar to staff.

East London line conditions

Maintenance of the East London line, including track, civil works, signalling, power supply, telecommunications and radio, is contracted to Carillion. The maintenance contract began in 2010 and is due for renewal shortly.

In London Underground days, the line was fitted with trip cocks, but these were not required once the line was re-signalled for main line use and AWS and TPWS train protection systems were installed.

London Underground had introduced radio communication using its ‘Connect’ Tetra system, but this was replaced by GSM-R as used throughout the London Overground network. The radio transmission is borne upon radiating cable and tunnel-mounted antennae in the underground sections.

The control centre for the line is at New Cross Gate, which is also the depot for train stabling and maintenance. South of this point, towards Croydon, the control interfaces to the Three Bridges ROC while the new link to Clapham Junction from Surrey Quays requires an interface with the Wimbledon signalling centre. At the north end of the line, the train service does not go beyond Dalston or Highbury – passengers beyond these stations needing to change trains. The line is therefore almost self-contained.

The Brunel twin tunnels, having had major maintenance work in recent years, are remarkably dry. However, the double-track tunnels to the north and south are very wet in places and, whilst pumps keep the tunnels clear of surface water, it is not a good environment for exposed telecommunications systems. The area around Canada Water is typical of these bad conditions.

Maintaining a pinch-wire system is thus a constant challenge with corrosion and dampness meaning that the system needed regular visits to clean, dry and often replace the pinch- wire components.

Challenging the standard

Before the days of radio communication, the pinch-wire system was the only means by which drivers could communicate with the control room. Now, with the introduction of GSM-R, drivers use the radio instead and the reliability of the system is very good. An analysis revealed that the pinch wires were rarely used. So could the system be removed, thus avoiding an expensive renewal?

A proposal was put to the ORR by TfL and, providing certain conditions were met, it was agreed that the pinch wire system could be removed. A tunnel telephone system, however, had to be retained so that staff and travellers at stations had easy access to the control room in any emergency. The GSM-R radio was considered robust enough for drivers to use should they need instant access to the controller.

The renewal project

Carillion, therefore, put in place a renewal plan to install a new high- specification telecom cable throughout the tunnel sections. To this would be connected the existing tunnel telephones and the system would terminate on its own concentrator, with a red handset, at New Cross Gate control room.

The cable is two pairs of 0.9mm conductors, double-sheathed and with an aluminium foil between the sheaths, terminated in weatherproof boxes supplied by Abtech of Sheffield at the telephone locations. The phones are the normal weatherproof type supplied by Ford Electronics. Calling control is achieved by lifting the handset, as in a standard, central battery operation.

The new cable was run in during 2016 under night-time possession arrangements – typically only three hours long – using rail mounted trolleys as these were seen as safer and more flexible than a road-rail vehicle. The three-kilometre section took two weeks to complete.

After an independent test of the system, carried out by Atkins, the system was commissioned on 21 December 2016, just before Christmas, and the drivers’ portable handsets were recovered. Much improved speech quality has resulted. Maintenance requirements are now minimal, with checks programmed for five times per year instead of every week, thus saving considerable expense.

Use of the GSM-R radio for emergency purposes is by pressing the red button that immediately alerts the controller and prioritises the call over any others that are in progress. The signaller can immediately switch off the traction current by means of a ‘trip’ on the telephone system console or by contacting Lewisham Electrical Control Room on a direct-line telephone. A box on the signaller’s desk enables the trip to be reset once it is safe to do so.

Tunnel pinch wire systems are thus likely to gradually become a thing of the past, a logical step forward with the advance of technology.

Written by Clive Kessell.

Thanks to Nathan Methven and Rubel Miah of Carillion for explaining the project and circumstances.