There could be all sorts of answers to that one. If you want to gain a fuller understanding I would like to suggest a computer game called SimSig. Did I say game? Those of you who like lots of high speed action need read no further – this is not for you. However if you like the challenge of chess and other strategy games then read on…
SimSig is a simulation of a modern signal box and comes in a variety of areas of the UK Rail Network with associated user manuals to provide guidance. Each is supplied with a representative timetable for a specific era which normally covers a full 24 hour period. There are usually a variety of scenarios too to enhance the difficulty. A history of how SimSig came about can be read on the SimSig Wiki. When you know that the ‘game’ has been used for training real signalmen then you will appreciate that it is quite true to life.
I’m currently playing the Edinburgh simulation and here is a classic example of how a train can become very late indeed…
… The grey lines represent the tracks and the white shows the route that has been set. You can see the signals alongside the tracks. The red sections indicate the presence of a train. Sitting in the centre is 5G24 – the 05:17 Perth to Kirkcaldy empty stock working. When it gets to Kirkcaldy, it becomes 2G24 – the 05:57 service and first train of the day to Edinburgh. The red train on the right is the 1A25 Aberdeen service – running 3 minutes late for no reason other than the timetable is probably too tight on the section from Dalmeny to Cupar. On the left is the 5M49, running about 7 minutes early because it has time to spare to on its run to Dundee. What is supposed to happen is that the 5G24 should cross between the two other trains. Unfortunately, on this occasion the points failed when I tried to set the route after the 1A25 had passed. So the 5G24 is now stuck there until a technician can fix the fault – anything between 30 and 45 minutes. So it’s going to be very late at Kirkcaldy and there will be a lot of angry commuters! On top of that, its next journey will also be delayed and it will be quite some time into the day before it finally gets back into its planned slot.
So there’s one example of how a train becomes late. You have the full range of usual reasons too – signal failure, loss of power, police or ambulance attending an incident, wrong kind of catering trolley (Don’t laugh, it does happen!), broken window, etc. The only thing that isn’t simulated is a locomotive failure. So whilst the majority of passenger trains will run in their planned slots there will be some that run late and you will need to minimise the delay whilst ensuring that you don’t delay the other trains that are on time.
Now the bad news… Freight trains! Like passenger services they have a timetable. Unlike passenger services – if you find one that is making a pretence of running to that timetable then you should check if your watch has stopped 🙂 Freights run on a heady mix of African time and anytime will do! They can run early (sometimes very early) or late so, again, you need to fit them in as best as you can amongst the passenger services and watch out – sometimes a Freight needs to use the same platform as a passenger service and you can wind up with the passenger train blocked as a result.
Additionally, you are generally looking after a section that would normally be overseen by half a dozen signalmen so you’re guaranteed to be busy! Hopefully, you can see where the challenge lies 🙂 They’re free to download and don’t take up a lot of disk space. The simulations run in real time but if it’s too quiet in the early hours of the (simulated) morning you can always speed it up. You might want to if you are working Cambridge, but you won’t for the North London Line or the Edinburgh simulations. I usually find an hour at a time is long enough for a session and I then save where I got to for the next time.