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London Underground Headcodes

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LUYMun

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Within the main railway network, there is a standard classification of rail services comprising of a headcode, which comprises of three numbers and an alphabet (e.g. 1Z99).
In the London Underground, there are different system of classifying tube services, made up of three numbers (e.g 366). I notice this when I read the Underground's Working Timetable (WTT), especially when some services have a 'D' after their number or any letter before it.
This is something I do not fully understand on how it works. Could someone please explain how this form of headcoding works?
 
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Domh245

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They aren't headcodes so much as train reporting numbers, or in effect unit diagrams. All entries in the timetable under a certain Train number will be run by that train with individual trips recorded in the row below under "trip number" - although only the train number tends to be used on the ground, being displayed on the front of the train. Generally they'll be grouped by service, so for example on the district line all 07x services are Wimbledon-Edgware Road, 12x services are peak-only services, etc

A 'D' suffix indicates a de-icing train and should be allocated de-icing capable units as a result. Letter prefixes indicate a service on another line, so in the district line timetable, anything appearing as "H2xx" means it's a Hammersmith & City/Circle line train, although the 2xx number is a giveaway anyway
 

Harsig

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The three digit number might more properly be regarded as a diagram number. i.e. once a train is allocated to that diagram it runs with that three digit number all day and is referred to by that number. To uniquely identify a particular journey, you also need to refer to the Trip Number, which is also shown in the WTTs. In general a single trip is deemed to last until the train reverses, at which point it begins a new trip, normally, but not always, numbered one higher than the previous trip. (Special arrangements apply to the Circle Line where trips are deemed to start and end at Aldgate, even though the train does not reverse there)
So for example 401-01, which is Train 401 trip 1, on weekday is the 0542 Rickmansworth North Sidings to Baker Street, while 401-02 (Train 401 trip 2) is the 0631½ Baker Street to Amersham, and so on throughout the day until 401-18 (Train 401 Trip 18) which is the 0133 Uxbridge 25 Road to Uxbridge sidings.

Generally each line is allocated a block of three digit numbers to use, selected where appropriate to avoid conflict with other lines with which they may interwork.
As to the letters that may or may not appear, the following applies:
D. If this appears after the three digit number then this indicates that the train allocated to this diagram should be one that carries de-icing equipment.
Letters which appear before the number generally indicate a train which is shown in the line working timetable for information, but which is not actually a train associated with the line that the working timetable applies to. e.g. Jubilee Line Trains working in and out of Neasden Depot are shown in the Metropolitan Line working timetable with a 'J' prefixing their three digit diagram number.
 

Mojo

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Generally each line is allocated a block of three digit numbers to use, selected where appropriate to avoid conflict with other lines with which they may interwork.
It’s also worth pointing out that Night Tube trains (ie. trains that run during normal traffic hours on a day and stay out beyond close of traffic have their own numbering system) that is different from conventional train numbers on that line. For instance Central line trains are in the 0 and 1 hundred series, whereas on Friday and Saturday traffic days trains staying out overnight are numbered in the 2 hundred and 3 hundreds.

Train numbers don’t end in 8 or 9. For instance after train 236 is 237, then 240 (if the line has that sequence). People might want to read this really good article on Programme machines here http://www.metadyne.co.uk/pdf_files/Automatic_Junction_Working.pdf

Whilst set numbers should stay with the specific compo for the day, it is possible during service disruption, or if say a depot requires a certain unit for a certain time, for the service control team to arrange a reform (this is when they will change the number into another number) or a stock and crew (this is where the Train Operator will take their number and themselves onto another train and vice versa).
 

Dstock7080

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When LU trains operate over Network Rail regulations and signalling, train numbers are converted into the NR reporting number system for use by signal operators: ie. 2C62 for a Tower Hill train and 2E74 for an Edgware Road.
 

bluegoblin7

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Train numbers don’t end in 8 or 9. For instance after train 236 is 237, then 240 (if the line has that sequence). People might want to read this really good article on Programme machines here http://www.metadyne.co.uk/pdf_files/Automatic_Junction_Working.pdf

Also worth pointing out that as lines are modernised the restrictions around using 8s and 9s are slowly disappearing, although most lines stick to tradition. The notable exception is the Central line, which runs its Sandite/Rail Adhesion Trains as 488/9, and is currently using a 9xx series as part of the special timetables.

5xx and 6xx series are generally reserved for Engineering/Ballast trains, whilst the 7xx series is for Test Trains and stock moves etc.

A few other ‘special’ numbers:
-771-4 are used for Tamping Machines.
-775 is generally Auto Visual Inspection Trains
-776 is the Track Recording Train
-777 is often used for weedkilling trains

Heritage trains using the 1938TS often run using 745/6/7, since 2013 most Sarah/Steam hauled specials have used 150.
 

rebmcr

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Special arrangements apply to the Circle Line where trips are deemed to start and end at Aldgate, even though the train does not reverse there

Surprising that wasn't revised to Edgware Road when the Circle line started running to Hammersmith. Was it a case of old equipment not being worth modifying?
 

bluegoblin7

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There’s no technical reason why that couldn’t have happened with the various legacy signalling systems, but would have been a faff when trains were extended or short tripped due to service perturbation (most commonly to Moorgate). Arguably the trip numbers are most crucial for the signalling computers operated from Baker Street Signal Control Centre - as this control(s|led) from Baker Street up to and including the Aldgate triangle it’s a very logical place to split trips up. The older technology at Earls Court and Edgware Road is/was less reliant on trip numbers.
 

TiedUpInNotts

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I was told there is never a train numbered 100 running on the Undergeound because it sounds like the term "one under" and could cause confusion during communication of misheard. Not sure if this is just urban myth.
 

Lewlew

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I was told there is never a train numbered 100 running on the Undergeound because it sounds like the term "one under" and could cause confusion during communication of misheard. Not sure if this is just urban myth.
When referring to a train number in any safety critical way it'll always be announced as One, Zero, Zero instead of one hundred.
 

Dstock7080

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