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All the trains on the London Underground have a number on the front, which I've learnt is called the "set number". I've noticed that the trains on each line tend to have numbers which are close together. (For example the District line trains often have numbers in single or double digits, whilst Piccadilly line trains are usually around 2 or 3 hundred).

What are these numbers based on? Is it the line that the train is on, or is to do with the rolling stock used? I know most lines have use their own set of rolling stock, but in places where they don't (eg District line trains to Edgware Road), which set numbers do they use?

Also, if anyone could point me to a list of the exact ranges of set numbers used, that'd be much appreciated.

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The place to find the definitive answer is "District Dave's London Underground Forum" – TheMathemagician Aug 28 '14 at 15:32
up vote 8 down vote accepted

One of the few (or rather the only) explanation I can find on the "Set number" is from

Another number which appears on the train is the "set number". This is displayed at each end of the train to identify its duty in the timetable. The number is set up by the crew preparing the train for service and it is retained by that train as long as it works that particular path in the timetable for that day. It provides a useful means of quickly identifying trains and is used whenever reference made to particular service trains.

So long story short it's a train number like "Pelham 123" basically identifying the route the train is running today including line and schedule, though if you feel like a project you can take a look at data from Trackernet to figure it out.

Possible explanations for train set numbers

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The Trackernet data is actually what got me wondering about this. The documentation is quite sparse about this type of thing. It gives no explanation about what a set number is - I originally thought they'd be unique for the whole network, so was surprised when I saw a given set number jump from one line to another. – lucas Mar 23 '13 at 18:25
@lucas the Tube has several types of equipment, each type used on a specific series of lines (iow, a specific type of train will only run on a specific set of lines, not any other). I'd not be surprised if set/train numbers have overlap between material types, as the crews would never be confused about it, the complete identification being material type + set number. – jwenting Mar 25 '13 at 7:40

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