RAILWAY OMNIBUS CIRCUITS
1. The system described
Those unfamiliar with traditional telephone arrangements on British railways can be forgiven for assuming these were not dissimilar from those of the public network. A little thought soon dispels this notion. Public exchanges tend to serve relatively densely populated areas in which the majority of telephones to be served lie within a short radius of the exchange, generally about three miles maximum. Most railway telephones, however, are strung out along the routes taken by the railways, at each and every station, depot, signal cabin and other installation. To serve all these from an exchange located at the central point of a local community of interest would be hopelessly impossible; it would work in major cities and around large junction stations but not along the rest of the routes. Exchanges would be needed every six to ten miles, which would be uneconomic.
The policy adopted until, say, twenty or thirty years ago was to establish conventional exchanges (manual or automatic) at regional and divisional head offices, at major engineering works and at important stations. Other locations were served by long party lines connected at one or both ends to a railway exchange. Unlike on normal party lines, the telephones on these circuits could ring one another or the exchange. Ringing on these lines was manual, employing separate ringing codes—akin to radio call signs—for each way station on the circuit.
Latterly, particularly in the 1970s and 80s, some of these manual party lines were converted to automatic working (with special arrangements allowing one user to dial another); that was chiefly on the Southern, Western (a few circuits on the London Midland and Scottish Regions were also converted using the Auto Rescall system). The majority of party line circuits were abandoned altogether, however, and replaced by normal dial telephones connected to 'add-drop multiplexers' on carrier transmission systems.
Although we have used the term party line for sake of explanation, that name was not normally used on the railway. Instead the term 'omnibus' circuits (omnibus being the Latin word meaning 'for everybody') was used. Most staff called the telephones the 'bus' phone or the 'circuit' phone.
Another difference from normal telephony was the fact that most omnibus circuits used direct current (DC) ringing; a few very long circuits, mainly on single line railways, used magneto (AC) ringing and technically these were more correctly called 'bridging circuits' (as their bells bridged the line).
Omnibus circuits were first introduced in the latter decades of the 19th century, when many telephones on the public network also used DC ringing. The system had the advantage of lower initial cost; the cost of a magneto generator at each telephone for calling was avoided and instead only a battery and a ringing key (press button) was necessary. Railway companies were always short of capital, making the solution with the lowest cost also the most attractive. Accordingly the railways started with DC ringing and remained faithful to it for 100 years or more.
DC ringing (or battery calling) had the disadvantage that when several telephones were connected on one pair of wires it became very difficult to ring all the bells connected in parallel. The solution was to place the bell in a local circuit operated by a high-sensitivity relay connected to the line. This reduced the battery strength needed at each telephone to ring the other way stations on the line but in practice most circuits needed ringing batteries of 24-30V (in addition to the 3V needed to feed the microphone and 6V for the local bell).
The codes used for calling stations along the line used either combinations of long and short rings (e.g. - . - ) or else a number of rings separated by pauses (e.g. 2-4-1). Exceptionally on the Western Region and its predecessor the Great Western Railway, callers would indicate the first digit of the code by turning a selector switch to the required digit (1-8) and then sending the second, numeric, portion of the code.
Some telephones had two or four ringing buttons instead of just one. Where two were provided (or a lever key capable of moving in two different directions), one button (or position) was used for normal code ringing and the other was used to call Control or the parent exchange. Where four buttons were provided, one key was for normal code ringing and the other three were assigned special functions.
At some locations (mainly signal cabins at junctions) switches were provided, allowing one circuit to be connected to another. Separate ringing keys were provided next to the telephone in some places to call a single location. On the Southern Region switches were sometimes provided to disconnect the omnibus telephone from its normal circuit and connect it instead to the nearest electrical control room.
The prime purpose of omnibus circuits was for straightforward intercommunication between the stations, offices and signal cabins connected. They followed the line of route and seldom had much more than a dozen telephones on the same circuit. Most circuits terminated at one or both ends at a railway telephone exchange, where an operator could connect callers to other railway telephones (but not, by agreement with the Post Office, to outside lines). In some cases the omnibus circuits functioned also as 'junction' circuits between exchanges where a dedicated trunk line was not provided.
3. Code calls
Once allocated, the codes allocated to a particular circuit tended not to change (some locations might disappear, for instance when a signal cabin was closed and new codes added as required). Code lists separated in date by 40 years or more have been found to have no significant variation. Old code cards frequently survived into recent times for this reason.
Another 'consistency' was where a location had telephones on two or more circuits; in these cases the location would have the same code on each circuit for ease of recognising calls for that location. In general a separate telephone was provided for each circuit, so it is normal to see photographs of signal cabins with half a dozen telephones side by side on the back wall. Occasionally, to save space in a cabin, a 'concentrator' was fitted instead, using one handset and an array of switches to allow the user to take or make calls on any circuit from the same instrument.
The ringing codes for calling other locations on a circuit were normally printed or typed on cards placed in frames and screwed on the wall next to the telephone. Some sample cards are shown at the locations shown below. Thanks are due to Alex Knapton for supplying many of these.
Although these details represent only a minute proportion of all the circuits and codes, they are nonetheless representative and are typical of codes used all over the railway network.
Standard designs of card
WR Birmingham area
WR circuits parented on Banbury
- Banbury-Bletchley Exchange
- Banbury-Honeybourne Exchange
- Banbury-Leamington Spa
- Banbury-Princes Risborough
- Banbury-Wolvercot Junction
- Banbury-Woodford Halse
WR circuits parented on Oxford
- Oxford Exchange-Honeybourne
WR circuits parented on Reading, Berks. & Hants. line, etc.
- Didcot local
- Marlborough Local
- Reading Exchange-Newbury Exchange
- Reading Exchange-Westbury Exchange
WR circuits parented on Slough
- Slough-High Wycome auto party line
Great Central and Met/GC line circuits
- Banbury-Woodford Halse
- Leicester Local
- Leicester-Loughborough & Lutterworth
- London (W) Control-Calvert Station Box
- London (W) Control-Harrow-on-the-Hill
- London (W) Control-Marylebone
- London (W) Control-Woodford and Banbury
- London (W) Control-Rugby
- Marylebone-Culworth Junction
- Marylebone-Grendon Underwood
- Marylebone local circuit M.1301
- Marylebone local circuit M.1304
- Marylebone local circuit M.1312
- Marylebone local circuit M.1323
- Metropolitan Extension Line
- Neasden-Grendon Underwood
- Neasden local
- Rugby-Grendon Underwood
- Rugby-Woodford Halse
- Woodford Halse-Banbury
- Woodford Halse local
GW/GC Joint line circuits
- Marylebone-High Wycombe
- Marylebone-Northolt Junction
- Paddington Exchange-Princes Risborough
- High Wycombe-Princes Risborough
LMR Western Lines, London Division, inner area
- Brent Junction-Sudbury
- Broad Street Inspectors
- Broad Street Local
- Dalston Junction-Eastern Junction
- Neasden Yard-Feltham
- Watford Junction Local
LMR Western Lines, London Division, outer area
- Bletchley-Banbury General
- Blisworth Local
- Rugby Control-Blisworth
- Towcester-Cockley Brake
- Towcester Local
- Bingham G.F.-Saxondale Junction
- Spital Junction-Huntingdon
- Tuxford Central-Dukeries Junction
- Werrington Junction-Littleworth
- Warrington-Kenyon Junction
- Bargoed North-Rhymney
- Bristol Control circuit no. 8
- Carmarthen-Pembrey East
- Gloucester East-Gloucester West
- Gloucester Loco local
- Pembrey East-Burry Port
- Plymouth Control circuit no. 13
- Shrewsbury-Craven Arms
- Tavistock Junction local
- Glasgow Central-Edinburgh
Mystery signal cabin interior.
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