The Branch Line Society


Metropolitan Line Signal Cabins Part 2
Thursday 1st October 2015

All images © Andrew Gardiner 2015

On a beautiful sunny day the group of 12 (one impressively travelling specially from Anthorn, North West Cumbria) met at 10.00 at Amersham station in Sir John Betjeman's Metroland. Amersham signal cabin opened during 1960 for the extension of Metropolitan electric services (track energised from 2 Sept 1960). It has a route setting 'push-button & switch panel' which operates in a similar way to a 'one control switch' panel i.e. a separate button or switch for each route. The buttons operate routes for main/running signals and the switches operate routes for shunting/subsidiary signals. Signal aspects are repeated on the control panel and on the diagram. The panel has two sections; the left for the Amersham area and the right, a later addition, controlling Chalfont & Latimer station (where the former Chesham bay P3 is disused) and the Chesham branch. At both locations there is an 'interlocking machine room' which is in effect a slave Westinghouse Power Frame pneumatically operating the levers based on the route selected by the signaller. As well as the Met, the cabin controls Chiltern Aylesbury to Marylebone services in the area. A NR VDU Train Describer is present in the cabin but train descriptions are converted automatically between the signalling systems.

The 1960 vintage Amersham panel; Great Missenden (and Aylesbury) is left, Chalfont & Latimer right with a Southbound train to London shown at the latter.
There are also two trains at Amersham (P1 & P2) and one on the Chesham branch.

Group photograph, on the steps of Rickmansworth Cabin at the north end of the station, the former water tower behind lit up by the bright morning sunlight.

Rickmansworth cabin was next, opened in 1953 with a 47 lever Westinghouse Power Frame and various other operating systems. The power frame operates in the conventional manner with separate levers for points and signals. There is the facility for automatic working to be introduced in the area controlled by the frame by the use of two king levers; one for the northbound route and the other for the southbound route. The signal operator first clears the respective signals and then reverses the king lever. Signals then reset automatically for successive trains without the need to operate any levers. This was seen in operation on the northbound line but control has to be returned to the signaller to deal with a terminating train (from the south via the London end facing crossover into southbound P2).

Rickmansworth Frame, on the diagram this station is far left and Moor Park is off to the right. The illuminated track is clear and a train can be seen approaching Watford (Met) P1, the double track 'PSUL' Watford North to East Jns curve can also be seen right of the five Rickmansworth South Sidings.

Watford (Met) station is controlled by a programming machine at Rickmansworth. This is housed within the original cabinet which formerly contained plastic rolls with the sequence of trains for the day. These were read by the machine which then set the routes accordingly and is now digital with details of movements for several days. There is an override facility for any additional or cancelled trains as the machine otherwise assumes that trains arrive and depart in a fixed sequence. Watford South Jn (Met) is operated from Rickmansworth by a push-button panel as at Amersham. Finally, there is a small switch panel to control the stabling sidings south of Rickmansworth station. It only operates the points so care is needed before authorising drivers to depart and to ensure arriving trains are signalled onto the correct siding. Amersham and Rickmansworth both have the electronic equivalent of a train register book where the times of movements at key locations are recorded automatically. Interestingly this system is only used at these two 'quieter' locations as it is deemed too time consuming and impractical for busier signal cabins which still record times on special paper sheets!

The 99 steps up to Harrow-on-the-Hill cabin gave the impression of the inside of a lighthouse.

Catching a fast Chiltern train, the group travelled to Harrow-on-the-Hill. Taking breath after climbing the 99 steps from the platform up to the operating floor (very reminiscent of a lighthouse spiral staircase), the group were able to view another (1948) Westinghouse Power Frame. This operates very differently to Rickmansworth. The lower numbered end of the 95 lever frame contains 'push & pull' route setting levers. These sit in a mid position until they are pushed forward into normal or pulled into reverse at which point they will set the respective route. The higher numbered end of the lever frame is in effect an interlocking machine room pneumatically moving the required levers for the route selected. The route setting levers also drive two additional 'interlocking machine room' (IMR) frames at Harrow North (44 levers) and Harrow South (33) subsidiary boxes.

Part of Harrow-on-the-Hill frame, see link above for more pictures including route diagrams.

There is also a push-button panel for Northwood IMR which normally operates in automatic mode with routes set for straight running on the fast and local lines. Both Rickmansworth and Harrow-onthe- Hill have London Transport style illuminated diagrams which are unusual as a lit section of track is clear and an unlit section of track is occupied by a train. This takes a bit of getting used to. As with Amersham, the cabin fringes NR's Marylebone IECC. Even outside the peak, the signal operator was constantly occupied, which is why the traditional paper recording sheets were better suited to this busy location. In the peak, there are two signallers. The 99 steps were easier in the 'Down' direction!

The final visit was Rayners Lane, which has three separate push button panels on the same console for controlling Rayners Lane, Ruislip IMR and Uxbridge IMR. The push buttons are recent additions and were previously switches of the type used on a telephone concentrator (switchboard). The 'Rayners Lane' area controls the Metropolitan Line/Piccadilly Line junction and the turnback siding. In some circumstances, the signaller can pre-select the next route before the current movement has been completed. When it is safe to do so, the system will set this 'preselected route'. This allows the signaller to move onto another task, which is useful at busy locations such as this with up to 15 trains on the screens at once. Ruislip panel has a crossover and reversing siding for turning back trains and is also the headshunt connection into Ruislip Depot on the Central Line. The signaller also controls access to Uxbridge Depot, the station and its information system, advising passengers of the first and second departures as well as platforms for the next Metropolitan and Piccadilly Line trains. Piccadilly Line passengers can also be advised to catch a Metropolitan train and change at Rayners Lane if necessary.

Rayners Lane area panel for the Metropolitan/Piccadilly lines junction and turnback siding.

The signallers were very accommodating and keen to explain operations at their busy locations. After a most interesting and enlightening morning, Liz was thanked for being an excellent host and the group split up; some with shorter journeys than others. Special thanks to our member Rob Davidson too.