The Brighton line between Balcombe Tunnel Junction and Copyhold Junction is the southern equivalent of the Welwyn bottleneck on the East Coast main line. From just south of Three Bridges, the line reduces from four tracks to two through the tunnel and then over the Ouse Valley viaduct before opening out again to four tracks into Haywards Heath station.
The line was resignalled in 1982 under the control of the new Three Bridges Power Box, which covers from Croydon to Brighton with fringe boxes on the various branches. The technology used route relay interlockings, tungsten bulb signals, reed track circuits and a traditional FDM (frequency division multiplex) system for remote control of the relay rooms and indications. The twin-track sections at Balcombe and between Haywards Heath and Preston Park, near to Brighton, were equipped with SIMBIDS (Simplified Bi-Directional Signalling) as a means of allowing trains to run on the wrong line under restricted long block section conditions. This proved to be troublesome and had adverse safety implications as it was not possible to inform staff reliably that trains were running ‘wrong road’.
The facility was therefore never properly used. Now over thirty years old, the general condition of the signalling was showing its age and renewal was due.
The Balcombe area suffers from capacity issues and increasing capacity to six trains an hour in bi-directional travel has been essential to meet the increasing demands of the infrastructure but also to increase access to undertake essential infrastructure maintenance throughout the route without the need to disrupt large sections of the Railway. Balcombe tunnel is very wet and in poor condition. In recent times, masonry falls have needed urgent attention with the line being closed for lengthy periods, resulting in considerable disruption to train services with a lengthy diversion for through services or bus substitution.
A metal shielding has been attached to the tunnel roof, primarily to divert water away from the tracks and into the drainage channels and also to provide some protection against any further masonry dislodgement. The result is a decision to resignal this section of line to permit full reversible working and to provide more resilient equipment against the effects of lying ground water. It also will allow six trains an hour in each direction when reversible signalling is in operation and permit access to undertake essential infrastructure maintenance across the route without the need to disrupt this section of railway in its entirety.
The development of the scheme has been protracted with a number of false starts. Since the project involved only a partial resignalling, with the interlockings at Three Bridges and Haywards Heath being retained, the design work would have to delve into existing records in order to modify the relay circuitry. A contract to carry out the work was awarded to Kier as main contractor. Although a new name in signalling, the company has, in fact, a depth of experience in the discipline following its acquisition of May Gurney. The company has also undertaken signalling projects in East Anglia, namely Ely West Curve, Bury St Edmonds to Chippenham Junction, Ely to Peterborough track circuit replacement and Kings Lynn signalling renewals.
Although Kier has a growing in-house design resource, it also partners with other companies to provide additional expertise. One such relationship is with TICS Rail Signalling, based in Doncaster. Having worked together on various projects for nine years, the combined skills of Kier and TICS allow them to provide an enhanced product capable of tackling much larger signalling renewals schemes, offering Network Rail a combined signalling design facility, signalling installation delivery units and the substantial works testing teams provided by TICS.
The work entailed in letting the contract to permit full reversible working on both lines, Network Rail originally anticipated that only the track circuits and signal heads, and the associated wiring, would need replacing with the trackside location cases themselves being reused. However, a detailed survey showed that this was not feasible and thus the scheme was expanded to a complete renewal of equipment over the 9km section. The track layout is unchanged and thus the existing point machines were kept and also some signal gantries.
Report of Balcombe project kindly reproduced from the The Rail Engineer