Signals Flashing?

[O L Leigh]

Not quite, the situation at Colwich was that the first junction signal (down fast to down slow) was a single steady yellow. The driver wrongly assumed that having seen the flashing yellows this would mean the line was clear all the way through the junction and did not expect to see the next signal (down slow to down stoke) at red. The sequence was NOT 2 flashing yellows, 1 flashing yellow, red.

Correct.

Getting flashing yellows does indeed mean that the diverging route ahead has been set and that you are clear to proceed across it. How far you are permitted to proceed will depend on the aspect being shown by the junction signal, but you must always assume that it is showing single yellow until you actually get sight of it and be prepared to stop at the first signal after the junction which, if the junction signal has not cleared up from single yellow, will be a red.

O L Leigh

 

[BR 1979]

As an old-hand driver once told me; there is no such thing as an approach controlled signal.

This is incorrect, Many routes are set through Junctions with the controlling Junction Signal held at danger until the train has been on the approach track / tracks for a specified time, governed by a timer relay. Obviously only in RRI or SSI signalling systems although the same principle is used on mechanical signal boxes , the difference being that the signal lever is locked and cannot be pulled until an approach track has activated a timer relay which when it is timed out releases the lever lock. Maybe that is what the driver meant ?

And then we have 'auto sections' with route selection but that is a whole new thread

 

[O L Leigh]

I think what the old driver meant was to never assume that a signal will clear now matter how often it does, and to treat a red light as the absolute limit on how far you can proceed.

O L Leigh

 

[ralphchadkirk]

I think what the old driver meant was to never assume that a signal will clear now matter how often it does, and to treat a red light as the absolute limit on how far you can proceed.

O L Leigh

Correct, I am also lead to believe that it is a common cause of spads that drivers assume the signal will clear as they get close, and when they realise it hasn't they will be going too fast/to close to the signal to stop in the rear of it.

 

[hairyhandedfool]

Thameslink were (before FCC, but maybe still now) telling new drivers that, no matter what other drivers tell them, approach control does not exist, but I actually think this is to help prevent drivers assuming the signal will change.

The Colwich accident saw one change to the rules as I understand it, that, where there are 'two part junctions', flashing yellows will only be shown where the route across the 'whole junction' is set.

 

[Metroland]

Flashing yellows are all over the place these days, even through some quite low speed junctions into platforms and goods loops. Standard approach control is quite restrictive, and valuable minutes can be saved in schedules. They tend to be much more standard for newer schemes and were first used at Didcot East in 1979.

 

[The Planner]

We can only take advantage of them though if there is a big enough margin on conflicting moves a lot of the time. If an opposing train is too close then they will revert to bog standard approach release.

 

[Clip]

Theres normally a double yellow flashing when leaving Denham approaching West Ruislip but only ever seen it in the morning..

 

[BR 1979]

Correct, I am also lead to believe that it is a common cause of spads that drivers assume the signal will clear as they get close, and when they realise it hasn't they will be going too fast/to close to the signal to stop in the rear of it.

Apologies then , I was being a technical pedant. What you say is correct and assumption on the railways has led to many SPAD's and indeed disasters.

You will see there is a photo in my album that shows all to well what happens when a driver assumes a signal will clear and does not.

 

[ralphchadkirk]

Apologies then , I was being a technical pedant. What you say is correct and assumption on the railways has led to many SPAD's and indeed disasters.

You will see there is a photo in my album that shows all to well what happens when a driver assumes a signal will clear and does not.

No worries We're all pedants on here!

 

[moggie]

Here's my penny worth in an attempt to clear up any mis-understandings;

The rule book as it applies to drivers does not discuss Approach Control (which is not approach Locking which is something else entirely!!! - but then ANY signal engineer would know that wouldn't they).

Flashing aspects (FA's) are a method of signalling control which enables the driver to optimise control of their train on the approach to a diverging junction in the knowledge the junction is set AND CLEAR beyond the junction protecting signal.

This former provides (allegedley) benefits to performance.

Speed differentials are defined but change fairly regularly depending on individual needs / locations.

There are additional controls required which may inhibit the display of a FA based on the status of the signal beyond the junction ( we know this as the 4th signal in the aspect sequence). This signal is generally to be set and clear (controlled signal) or 'ready' to clear excepting a preceeding train in route. I.e no CONFLICTING movement taking place beyond this signal. The latter is a SPAD risk prevention measure which I believe dates back to an incident at Swinton. Standards have been amended on this element in recent times therefore inconsistent application remains on the network.

There are strict rules to prevent intermixing of FA sequences for different junction.

The Colwich FA sequence (if my memory serves me correctly) was flawed (although at the time technically compliant) because it provided an inconsistent arrangement to that at the nearby Norton Bridge Jcn which lead to the confusion of the driver at Colwich who used both junctions.

If a driver receives a flashing aspect then they are clear to proceed at least towards the signal beyond the junction on the divergence.

The junction signal aspect is the only information that the driver needs to observe to determine the aspect being displayed at the next signal beyond the junction.

A FY at the signal approaching the junction signal does not display sufficient information as to the display of the signal beyond the junction as it's aspect is determined by the aspect of the junction signal. Once the driver is past the FY signal, the junction signal may step up to a less restrictive aspect than Y (plus route indication) depending on the aspect displayed at the next signal beyond the junction. Hence the need to apply controls for the 4th signal.

The junction signal cannot be at red where a FA sequnce has been displayed on the approach. The only exception would be a signal irregularity caused by equipment malfunction or emergency route cancellation beyond the junction. Either way the junction would be locked and protected by Approach LOCKING.

If the controls for a FA aspect sequence are not present the signalling system will revert the junction control to Approach Control from red.


Happy to be corrected and I'm sure there are some historical 'special arrangements' around.

GK/RT0045 refers - nite all.