Lengths of loco hauled trains are quite easy for signallers to look up on the signalbox computer but multiple unit trains are, surprisingly, very hard. To find out the length of a multiple unit train on the IT systems available to a signaller, you’d need to search for a train on Web Gemini (TRUST will tell you vehicle running numbers but nothing more than that) to find out what unit/units is/are on it then look up the details for each individual vehicle in the formation to find the length of each and add them all together. That all takes quite a bit of time and assumes you have a log in for Web Gemini in the first place. That’s why many signalboxes have a locally produced table or spreadsheet handy showing the lengths of the most common different formations. Similarly, there is no easily accessible information about platform lengths available on the various bits of software used by signallers, so again locally produced tables/spreadsheets/diagrams are used. Nothing about it is easy or simple.
A contributory factor is that signallers are given no formal training at all about the different trains and traction types. None. Nothing. You just have to work it out yourself.
