Some years ago now I was involved in planning test trains in order to introduce a new fleet of trains to a UK TOC. It was a TOC that covered a vast area of the country, with stations in the 100's and a fleet of a similar size too. We often ran many trains, particularly through the night, to undertake various different types of testing. There was infrastructure testing (i.e electrics, signalling, gauging etc), operational testing (i.e signal sighting, platform-train-interface, stepping distances, platform sighting, stop board position etc) and a few other types.
Obviously, as part of these test trains, we ran some very long circuits depending on the nature of the testing. Some of them started late evening and then finished very early the next morning as sometimes that was the only way to get the job done efficiently.
On some occasions, I'd plan these long trains as one single path with one continuous headcode such as 5Z01 and on other occasions I'd plan them as consecutive headcodes such as 5Z01, 5Z02, etc. Generally, the convention is that trains that travel over the same location twice should have separate headcodes. Otherwise, when the train passes the location for the second time it will overwrite the time showing for the first pass, and the time for the first pass 'disappears'. It is quite confusing to look at. Furthermore, headcodes should generally follow in order to make it clear for the signaller to see what the train forms next. As already mentioned, they also often change letter in order to show a change in route. A train may come into location B as a 5RXX but may go out as a 5SXX, simply so the signaller knows the route the train will be taking is different.
The only occasions when I planned a trip as one continuous path was for the following reasons:
- If the trains were doing something very unusual (as test trains often do), the second digit of the headcode should really be a 'Z' (or Network Rail sometimes use XQXX or 3XXX headcodes), to show the signaller that the train is taking an unusual routing that they should be aware of. Running it as one long continuous path (i.e just 5Z01) means that the entire route of the train can be seen easily in one go. That makes it a lot easier to see where else the train may be going should there be disruption or a change of plan on the night.
- When planning a very long test trip, it is easier to have the path open as one long continuous trip than having lots of individual windows with every different path open. For example, if you're testing platform A, B, C, F, H and J at station X, it can be easier just to see them all on the same path (so that you know which ones you have covered and when), rather than on all the individual paths.
- If I was planning the trip AND diagramming the crew too (i.e test driver), it was a lot easier to bear the crew in mind with it all as one path, again, rather than separate paths. For example, it is easier to see when the train starts, where it stops where breaks could possibly be taken, where drivers could be relieved if necessary, where trains could be looped/taken into depots if the time needed to be cut, etc. It was just easier to have one long continuous path so that I could bear the crew requirements in mind at the same time.
