Train Activities 2
Joining Trains
Let's start another New simulation for this, with a starting time of 06:28. That will allow 1 minute before 3R67 appears from Baldock. (Other trains such as 1C77 should be allowed to pass through in the meantime.)
3R67 terminates at Royston P1, where it joins 2C67 arriving at 06:40 from Cambridge. We can anticipate from 3R67's TD that it will reverse at Royston, just as 5R96 did, and this is confirmed when we click 2C67's berth to reveal its TT, indicating that it will continue on to Baldock after joining 3R67. Here, 2C67 has been stopped at K986 (not necessary, only for demonstration purposes) and is waiting to join 3R67.
| Question: The Train List tells us 2C67 has stopped, so why hasn't the overlap ahead of it been released, not to mention the TC behind it? Answer: The route between 104 and K986 is permanently set by 104's automatic feature (its stem is white, indicating a set route, and its blue button is solid, indicating its Automatic function is enabled). 104 shows a red aspect because 2C67 is occupying this block. 2C67 has indeed stopped but the overlap has not been released. |
Calling-on
Calling-on is the act of signalling an approaching train to move into a platform at low speed to join another train already stationary there. In our example we will be calling-on 2C67 to join 3R67. This is not quite as straightforward as it might appear.
Let's say that, to waste as little time as possible, we set an exit route in advance from Platform 1, between K980 and the next main signal, K976. We then call-on 2C67 by setting a route for it from K986 to K980; however, the train is blocked by a red signal at K984. Attempting to set a route from K984 to K980 displays the error message (in the Messages window) Route set from the exit signal - call-on not allowed.
Why is this not permitted? In the past, accidents have occurred, usually at night or in conditions of poor visibility such as fog, when the driver of an approaching train mistook the distant green of the exit signal as clearance to proceed through the station, failing to notice a train already there. For this reason, an additional form of interlocking termed Huddersfield Control was incorporated as a fail-safe method of preventing an entry signal such as K984 from displaying a proceed aspect while the exit signal does the same, no matter how experienced the signalman might be. SimSig has incorporated this safety feature too.
Note that Huddersfield Control does not just apply when one train is about to join another; it applies when any train is stationary at a platform and there is any other train behind it. To enable joining to take place, we first need to cancel the exit route from K980. Naturally, there will be a time delay due to approach locking (see below) after which the route will be released, not to mention a penalty for causing an unexpected adverse change of aspect (green to red) to the driver of 3R67.
Having cancelled the exit route from K980, we now set a route between K984 and K980, at which point 2C67 is called-on. Note that K984's main signal stays red, while its subsidiary shunt signal (arrowed) turns white to indicate clearance to proceed at low speed, just as in a siding, but on this occasion, along the main line.
While this is taking place, we might think it safe now to try resetting an exit route from K980. But again, Huddersfield Control interlocking steps in and forbids us, this time with the message Call-on route set from the signal in rear. In other words, as long as a call-on route is set, we are not permitted to set an exit route ahead of it, for the same reason as the previous message. In a way, this message is the converse of the previous one.
It should be noted that other errors can be made here too. For example, suppose 2C67's direction after joining happened to be Down (to Cambridge), rather than Up to Baldock. Should we try setting a route in advance between K983 and 103, we would be greeted by the message Subroute locked in opposite direction.
What does this mean? Platforms 1 and 2 at Royston are long enough to permit two short trains to join in them, hence if you turn on Track circuit breaks you will see that each platform's track contains two TCs. Even though there is no signal at the middle of the platform, the route between K984 and K980 is really comprised of two subroutes (let's call them near and distant), enabling a train occupying each one to depart in the opposite direction from the other if necessary. In our situation, 2C67 is moving Up into the near subroute of P1, while 3R67 occupies the distant subroute. As a result, the near subroute is locked Up, yet we are trying to set a route in the Down direction towards Cambridge; hence the error message.
Let's leave these trains to join, now that they're both stationary (the K984-K980 subroute has been released, as you can tell by the absence of a white stripe and that K984's stem is grey). The entries for both trains on the Train List confirms this. Now that the subroute has been released, you can set an exit route if you wish, but why not wait until joining is complete?
Note that there is no need to issue a command to "Shunt forward" or anything else to facilitate joining here. Joining is on the timetable, so will be automatic. By now, Joining is complete and 2C67 ready to depart, as shown by a flashing TRTS light.
Let's set the exit track and wave it goodbye. Oops - it's carrying the wrong TD! This teaches us that TDs are picked up from the front end, not the rear. It might have been smarter to cancel the rear TD and interpose the new one into the front berth while 2C67 was waiting at the platform. As you see from the Train List, SimSig knows the train is actually 2C67, even though the berth indication is wrong, again confirming that the berth display is really just a label.
All's well. We used K976's berth to update the TD, and cancelled the old one lest some other train pick it up.
| From the above we can see we should allow at least two signals between one train an another following, where there is a platform involved, to avoid the first calling-on error, which usually causes a significant delay due to approach locking. The second is less likely to be seen except when two trains share a platform, so this is usually when they are being joined. |
You will find other Train Activities in other sims such as Dividing Trains, Detaching Trains and Dropping Coaches, but since none of the trains in Royston's TT utilizes any of them, they are omitted here.
Back to Royston - A Beginner's Guide
Last edited by GeoffM on 15/09/2016 at 03:00