Design notes

The implementation here runs entirely in the browser (at least once all the files are downloaded). I have taken a few (hopefully minor) liberties with the implementation. Differences from the prototype include:

Addition of position lights at the platforms

In the prototype the signaller would have been able to look out the windows of the signal box and see trains waiting directly at the platforms. That's not possible on the simulation (there's no real room to add windows and anyway I don't have any suitable images to display even if there was space.

Not all of the repeater instruments added to the shelf

I added the instruments I understood, but I'm not 100% sure of the operation of the remaining instruments

Sounds not taken from the preserved box

With the coronavirus lockdown I'm unable to record accurate sounds from the preserved signal box. That said the bell and plunger sounds I'm using (from Alexander at Orange Free Sounds) do, to my ear at least, sound fairly reasonable

Ancillary lights omitted

I have consider adding the ancillary lights to the diagram (for example, the lights indicating the state of the automatic half barriers at Halterworth), but I'm not yet convinced that it is worth cluttering the diagram even further!

Train timings

Although I've based the train schedule based on modern day schedules, the timing of the trains for the various track sections is based on a guess. Some day I plan to spend a day riding the various passenger services and trying to record more accurate timings. In any event I definitely have either prototypical timetables or timings!

Programming Notes

Impressively (to me at least), a lot of the coding for the simulation is handled by the cascading style sheets. In fact the largest part of the code for the simulation (as measured by the byte count) is actually for the sounds used by the simulation! There is a fair amount of javascript that the drives the simulation. The code is based on my original arduino based hardware simulation, but I do think the javascript is, somewhat incredibly, easier than the corresponding C++ code. That said I may well end up trying to bring my development workflow more up to date - through the main benefit of moving from my Ant based build system would simply be the ability to use the latest javascript tools for unit testing - so it may just be that that I take a look at!

Current Version

This site currently has Romsey Signal Box Simulation Version 3.284.0 installed.

Bell Codes

There are several bell codes that the simulation recognises. These are:

General Codes

These codes are used to signal to the adjacent signal box that something that needs attention from that box

Train Offering Codes

These code describe a train to the adjacent box and offers to direct the train to the adjacent box

General Notes

The simulation is based on how the Romsey Signal Box was operated just before its closure in 1982. The simulation therefore uses BR standard bell codes and allows passenger services to use the eastern crossover points as these were electrically operated and locked.

Control of the Simulation

The larger you can make the browser window for the simulation the better. While I have attempted to make the simulation responsive to the size of its window, my main testing was done on a 1920x1280 display. On my tablet it looks reasonable and can be used. On my mobile phone it will display but it is very hard to use - particularly if the phone is in portrait mode!

To move a lever you can simply click on it. If the lever is unlocked it will move to its other position. If a lever is locked hovering over it (for those using a mouse) will display text indicating why the simulation has locked the lever.

To make a bell push simply click the large button. A gap between pushes of a second or less will be treated as a short gap, a long gap is up to two seconds. The remote boxes use a cadence of one second for a short gap and 1.5 seconds for a long gap.

To move the commutator between Normal and Line Clear or Train On Line click on the buttons (the greyish squares) next to the desired position of the commutator control.

If you want to see what the simulation thinks the remote box is doing, you can hover (again for those using a mouse) over the image of the remote box's bell to see what it is up to

To add a train or a complete schedule of trains to the simulation, choose the train or schedule from the pull down in the bottom right of the simulation. Once the Add button is pressed the selected train or schedule will be added to the simulation. The complexity of the task roughly increases from the top to the bottom of the entries on this pull down.

The simulation can be speeded up using the speed controls. This only affects the speed of the trains themselves, the timing of the bell code ringing will be unaffected by the simulation speed.

For those new to signalling

In absolute block working, a block section (or simply section) is a section of railway line between one signalbox and another – in absolute block, lines are paired, with an up and a down line which run in opposite directions.

The block instrument consists of a small cabinet; its front face displays two indicators — telegraph needles — and has a commutator handle (some early designs of block instruments had miniature semaphore arms instead of needles). The upper indicator shows the state of the forward section, on the line leading away from the signal box. The commutator is used by the signalman to indicate the state of the section approaching his signal box, and the lower indicator repeats the commutator position. All indications are repeated on a similar instrument at the other end of the block section, in the associated signal box. The commutator has three positions and each of the two indicators has three positions: normal (or line blocked), line clear, and train on line. Either integral to the instrument or separately mounted, there is a single-stroke bell and a bell operating device, either a tapper or a plunger.

In a simple double line configuration where the signal boxes are A, B and C in succession, the signal box at B will have two block instruments, one for trains in down and up direction in the section between AB (trains leaving station B and trains approaching station B), upper and middle part of the first instrument and one for trains in up and down direction in the section between BC (trains leaving station B and trains approaching station B) upper and middle part of the second instrument.

The signalling bell, also known as a block bell, is used in conjunction with the block instruments if the bell is not integrated with them. It is a single stroke design and relays the codes from adjacent signal boxes. Each bell has its own distinctive sound or tone to alert the signalman which instrument needs to be attended to. The bells are activated by a (large) push button to make the bell in the adjacent signal box. Each push of the button 'tings' the bell once. A sequence of tings is known as a bell code and the simulation recognises many of the BR bell codes.

Example block-bell exchange

An example is the process of signalling a train in the up direction (from A to C) past a signal box B. The signal box in rear is A and the signal box in advance is C. The block indicators at B are in the Normal position. The signalman at A "offers" the train to B by sending an "Is Line Clear?" code on the block bell; for example to offer an express passenger train, he sends four beats consecutively; an ordinary passenger train is offered by sending three beats, and after a pause one more beat, usually written as 3-1. If the signalman at B can accept the train safely (if there is no other train in the section, and the line is clear up to B's clearing point[3]) he "accepts" the train by repeating the bell signal, and placing the commutator on his block instrument for the section from A to "Line Clear". The "Line Clear" is repeated at box A, and allows the signalman at A to clear, or "pull off", his signals. In case the line is not clear, B simply does not acknowledge A's "Is Line Clear?", and leaves the commutator in the Normal position.

At this point, B will not clear any of his signals. Firstly, he cannot clear his starting signal without a "Line Clear" from C. As a result, B will not clear his home signal – he can only clear it when he either has a clear run through (which he does not have without a "Line Clear" from C), or is confident that the train will be able to stop at his starting (or section) signal (this is not done until the train is in view and visibly under control). Finally, his distant will not clear without both his home and starting signals being clear.

As the train passes the starting signal at A, the signalman there sends the "Train Entering Section" signal (2 beats) on the block bell to B, and the signalman at B acknowledges the signal and moves the commutator to "Train On Line". His lower indicator on the block indicator to A repeats the position of the commutator.

B immediately offers the train on to C, after calling for attention, by sending the "Is Line Clear?" bell signal (repeating the same steps A had done while offering the train to B); if C accepts it he repeats the bell signal and places his block indicator to "Line Clear", which moves the position of the upper needle indicator in B's block instrument to repeat that indication. B may now clear his signals for the train.

After an interval, the train will arrive and pass B; as it does so, B sends "Train Entering Section" on the block bell to C. Then C acknowledges the bell signal and places the block instrument to "Train On Line". As the train passes, he restores his signals to danger, and when the whole of the train passes B complete with tail lamp attached, B sends the "Train Out Of Section" bell signal (2-1) to A and when A acknowledges it, he places his block indicator to "Normal". The block section between A and B is now normal and A can offer B another train, if he has one.

When the train has reached C, the signalman there sends "Train Out Of Section" on the block bell and when B acknowledges it, C places the block indicator to "Normal".

Direction Lever

As the line between Romsey and Eastleigh was singled in 1972, a direction lever is used to control the single line. There is a direction lever in both the Romsey and Eastleigh signal boxes. When a train needs to be signalled through the single line, block bells are used in the same manner as for a double line. However rather than a block indicator being used, the direction lever is used instead. To indicate that a line is clear for a train, the direction lever at the far end of the line is pulled to make that indication. The signal protecting the entry to the single line cannot be pulled (to indicate to the train that it can proceed) unless the direction lever at that far end has been pulled. Once the far end has acknowledged that the train has entered the section, the direction lever is replaced to its normal position.

Text on absolute block signalling taken from Wikipedia and used under terms of the Creative Commons Attribution-ShareAlike 3.0 Unported License. The text used on this page was added to Wikipedia by Wikipedia users (and IP addresses) JonRoma, Denelson83, Afterbrunel, Signalhead, 86.190.37.27, Danny252, 1.23.79.179, 1.23.78.75, Just a guy from the KP, Sir Ross BA, BD2412, 90.241.210.52, 107.190.33.254, Hairy Dude, 86.190.37.150 and 81.77.124.158.