THE SIGNAL BOX

OVERSEAS

SPEED SIGNALLING
On the suburban lines of Melbourne

by John Hinson


Three position upper quadrant for speed signalling, at Brighton BeachCoo-er, that's a funny signal, what on earth do those indications mean?

Those were my thoughts on seeing signals such as this on the suburban lines of Melbourne. Three-position signals I could understand, but the function of twin arms defied me. Especially when they show indications such as this.

Fortunately, Andrew Waugh patiently explained the principles, and suddenly it began to make total sense. Indeed, it seems that the speed signalling in this area is very much on the principle as it was installed (from 1915), whereas elsewhere in Australia the indications given have got more comprehensive as the railways strived to make the indications more flexible.

The speed signalling described here exists in semaphore an colour-light form, but the indications given are the same. The semaphores are more fun, though, so there are more pictures of those here.


Speed signal showing "stop"Here is a speed signal showing "on", or "stop". That seems quite straightforward, but look closer. There is a red light mounted lower down the post.

This is because all speed signals show two indications. The top arm (or light) is for high speed routes, whilst the lower arm or light is for medium speed routes. The term low speed applied to shunting signals. It doesn't matter if they are left turns, right turns or medium speed routes straight ahead, if the move is for a speed of 25 mph the indication is given by the lower arm or lamp.

Anyway, at this location there are no divergences or speed restrictions, it is a piece of plain, straight line. Therefore, the "stop", "caution" and clear" indications are given by the top arm. The bottom arm (for medium speed routes) has no need to move, so all that is provided is a permanently lit red lamp.

Do you think it odd that every train here has to pass a red lamp? Well, visualise a conventional junction signal, such as the home signals illustrated at Bacchus Marsh. Those signals always show red in one signal when the other has been cleared. And that doesn't seem odd.

Incidentally, the signal can be identified as being "automatic" by the fact that the two lights are staggered and also by the pointed ends of the signal arms.


Close up of three-position signalA close-up view of this signal demonstrates how the spindle of the signal arm runs directly into the standard Westinghouse signal motor.

This compares interestingly with the three-position signals in the UK at Whitemoor yard which had similar motors mounted at the foot of the signal posts.


Three psoition upper quadrant signal showing "caution"Three psoition upper quadrant signal showing "caution"The signal illustrated above spends a considerable amount of its time in the "stop" position because it protects a level crossing at the next station and doesn't normally clear until trains have arrived in the platform. The next signal back therefore spends much of its life in the "caution" position.

The caution position is with the arm inclined at 45º and displaying a yellow light, as seen here.

Again, with no medium speed route applicable, a permanent red light is provided in lieu of a second arm.

One point worth noting is that the arm's light is to the left of the post, but the lower light is to the right. The staggering of the two lights is deliberate, and (I believe) specifically identifies signals as being automatic.


Three position signal in the "off" positionA train has arrived at the station, and after the crossing barriers have lowered, the signal mentioned above has cleared to "off" or "clear" for high speed. The red light below remains lit.

The train is typical of the suburban electric units, and the alighting passengers think I'm nuts.

They are probably right.


Colour light speed signalsYou should have followed things so far, so lets now make things more complicated. We are standing on Brighton Beach station looking up the double line towards Melbourne. The platform I am on is a dead end bay but it was once the terminus of the line.

To the left are sidings, whilst to the right, a later (also double track) extension of the line curves sharply away through two other platforms.

A departing train from the dead end platform would have to pass through the slip points to join the Melbourne-bound line. Likewise, a train from Sandringham curving in to the straight line would have to take the points at medium speed.

Therefore, both the signal in front of me in this view and the one behind the steps of the footbridge for the Sandringham line show similar indications, although one is a searchlight signal. The only routes for both signals are medium speed so here the top signal is a permanent red. The signal below will show red, yellow or green as appropriate. The Sandringham line signal is showing "clear" at medium speed, and if you look carefully you can just make out two automatic signals ahead showing "clear" ar high speed - green over red.

The signal facing the camera also has a miniature yellow aspect for low speed moves (shunting) below the other aspects, and all indications of this signal are repeated in minature at track level for trains too close to the main signal to have a good view.

The box here is switched out - and that's my wife Gill looking at the timetable to see if there are any trains booked in or out of the bay platform. There aren't, and the box is now rarely opened.


Speed signal at Brighton BeachAre you still following me? If you are, this signal should now make perfect sense.

No? All right, I'll explain.

But firstly, compare the two arms. Notice how the staggered aspects are achieved by different spectacle fittings.

This is the last signal before reaching the right-hand of the two in the above picture. That signal only ever showed a "stop" indication in the top aspect because all movements ahead of it were at medium speed.

Therefore the top arm here, applicable to high speed moves will never show anything other than horizontal or 45º.

However, the lower signal head (for medium speed moves) at that next signal can show red, yellow or green so the bottom arm here does the same.

Therefore the indications given by this signal will be:

If the section ahead is occupied - red over red Both arms horizontal - "stop"
If the section ahead is clear, but the next signal shows "stop" - red over red Top arm inclined at 45º, lower arm horizontal
If the section ahead is clear, and the next signal shows "caution" - red over yellow Top arm inclined at 45º, lower arm at 45º - meaning "Reduce to Medium Speed"
If the section ahead is clear, and the next signal shows "clear" - red over green Top arm inclined at 45º
Lower arm vertical

I don't know about you, but I still think it looks weird . . .


Comments about this article should be addressed to John Hinson