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Home » About » Signal Engineering

Alton Signal Box

The MHR signal box at Alton is the fourth and last one to be commissioned since the reopening of the line in 1977. The history of the box structure is not fully known but it could possibly be the original box at Alton that was closed in 1903. This old box was replaced by a larger brick LSWR Type IV building and the wooden upper storey of the redundant box was moved to platform 1 at Alton where at ground level, it served as the office for the Stationmaster for many years.

When the MHR acquired this structure from BR, it had only to be moved a few hundred yards to rest on its new brick base to the west of Alton station. This signal box is the only one on the MHR that is not located on a platform and it therefore has a higher ‘locking room’ structure. The operating floor is reached by a dogleg staircase with a landing halfway up which is used by the signalmen to exchange key tokens with both arriving and departing trains.

When first installed on its brick base, the box was equipped with a 20 lever mechanical frame. However it was soon realised that with a station loop and later a passing loop to control, a 25 lever frame would be required to fully control all the required movements. Also the Meon Valley Loop would have to been controlled from here and as the country end points were further than 350 yards (the limit for mechanical rodding) this end would have to be motorised and track circuits installed. This is what led to the thinking of using a powered signalling as opposed to mechanical.  As there was also a need to also operate Alton in a semi-automatic mode, an alternative signalling method had to be adopted. The result was the installation of a panel controlling colour light signals and electrically operated point machines.

Signalling installation work started with a small band of enthusiastic volunteers and over a 15 year period they installed all the lineside equipment required that included all the location cases, cabling, signal posts and colour light heads, point machines and track circuits.

The history of the panel’s console has been traced back to Three Bridges on the Brighton line and later to Chichester signal box from where it was retired before being acquired by the MHR. The panel is an IFS (Individual Function Switch) design whereby a separate switch is provided for each route that can be set for a signal. There are a total of 20 signal controlled routes utilising 2 or 3 aspect colour light signals, position light signals for shunt and subsidiary routes and eight power operated sets of points utilising electric point machines. The panel controls 1.8 miles of track from the shunting neck at the London end of the station, past the site of the old Butts Junction, to the start of the outermost track circuit towards Medstead which is 1.6 miles from the signal box. The 1.8 miles of track is covered by 18 track circuits that are of the AC type due the proximity of DC traction power on the Network Rail electrified lines in platform 1 and 2. Access is possible into Network Rail’s platform 2 via a crossover located between the signal box and the station. This is controlled by a ground frame that is electrically released from the panel.

The relay room is located in a REB (Relocatable Equipment Building) that houses all the necessary power supplies and in excess of 400 plug-in rack mounted relays. Wiring the relay room commenced in February 2009 and was finally completed early in 2010. The complete signalling system was then ready for rigorous testing by Atkins, a Network Rail infrastructure contractor and following a clean bill of health, commissioning took place on 3rd March 2010.   

As previously mentioned, the design of the Alton scheme required that trains could work the Medstead to Alton section without Alton box being ‘open’ – namely an “Auto Working” (AW) system for signals, points and the electric key token operation. When the Medstead signalman wishes to send a train to Alton, a single plunge on the EKT machine in Medstead box will result in an electrical release being obtained for a release of a key, given that the single line to Alton is clear. This allows the Medstead signalman to clear the Up Starting signal for the train to proceed to Alton.

The AW system is designed to deal with the following movements:

  • service trains from Medstead to Alton which require the locomotive to run round at Alton
  • service trains from Medstead to Alton which do not require a run round at Alton (e.g. DMU, top & tailed services)
  • getting ECS (empty coaching stock) from the sidings at the start of service
  • putting ECS in sidings at close of service
  • light engine calling-on to ECS in Platform 3

The AW system CANNOT accommodate these movements:

  • any movements into or out of the Meon Loop line
  • double headed trains where the locomotives are required to run round independently
  • any train requiring to run round formed of more than 6 passenger coaches or an equivalent length of alternative stock
  • any train formed of more than 7 coaches or an equivalent length of other stock

When the train occupies the outermost track circuit on the approach to Alton, the AW routes are ‘set’ and the signals clear to a proceed aspect to allow the train to continue into platform 3. If the platform line is occupied by empty coaching stock, the signals only clear as far AT55 just before the signal box. This signal is provided with two plungers that the crew of a light engine can operate to either set a route via a subsidiary signal into the occupied platform or alternatively to the station siding if the coaching stock has been berthed there.

On the arrival of a normal steam hauled train in platform 3, routes are automatically ‘set’ for signals and points to operate to allow the loco to run-round. Once this movement is complete, the crew insert the electric key token into a special instrument located on the platform that when turned, sets the route to enable points and signals to operate for the train to return to Medstead. It is therefore evident that under Auto Working, only one train can ever be in the section between Medstead and Alton.  

It should be particularly noted that the AW part of the system is a non – vital operation. This means that the basic security and integrity of the signalling system is provided by the relay interlocking in the Relay Room. The AW may request an operation but, if the safety conditions do not allow that to happen, the interlocking will ignore the request. Hence, the AW is not able to compromise the safety of the basic system as when the box is open.

During the latter half of 2013, Network Rail closed Farnham, Aldershot and Ash Vale signal boxes with control transferring to the Woking Area Signalling Centre (ASC).  Since the Mid Hants extension to Alton was completed many years ago, we have had a main line connection via Platform 2. Train or locomotive movements between us and Network Rail were managed verbally with Farnham, and latterly, the Woking ASC signaller. As part of the changes Network Rail has made, a new signalling “fringe” interface has been designed that provides new signalled routes across the NR/MHR boundary. This “fringe” work was successfully commissioned on 16th November 2014, and now enables Mid Hants signalmen at Alton to signal trains directly to and from Network Rail’s Platform 2.

The infamous white wooden gate that had denoted the boundary between the two railways was ceremoniously removed as part of the changes and has been replaced by a wooden anti-trespass guard.   

The MHR Ground Frame controlling the crossover into Platform 2 is electrically released from Woking ASC with a new AC track circuit installed through the crossover points that butts up to the Network Rail track circuit in Platform 2. The original Network Rail signal at the country end of Alton is now a 2 aspect signal capable of showing a yellow aspect and has been re-numbered WK459. MHR signals AT55 and AT57 that only controlled access into Platform 3, now also control movements into NR Platform 2. These two signals have both main and subsidiary aspects. The main aspects are fitted with Junction Indicators reading into Platform 2 when unoccupied. The Route Indicators for the subsidiary signals now indicate a ‘2’ for movements into Platform 2 if it is occupied.

The route setting and clearance of WK459 for movements onto the MHR, or AT55 / AT57 for movements from the MHR, is achieved by electrical ‘slot’ releases controlled from both the Woking ASC (Panel 3) and the MHR Alton panel.

Modifications have been made in the Relay Room to accommodate the additional multicore signalling cables and 44 plug-in relays that are required for the necessary controls and interface to the Network Rail Solid State Interlocking (SSI). The panel in Alton box has been modified to accommodate additional signal and release switches and for the display of new track circuit indications.

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