What causes signal failures in the UK?

[FrozenPoints]

Excuse my ignorance, I am just facinated by what causes signal failures.

I assume it is multiple factors.

From vandalism (cable theft) - which incidently caused much chaos to the line between Manchester and Preston via Bolton - meaning 1tph was effectivly running, trains terminating unexpectedly etc. And the Northern Rail conductor aptly put it yesterday on my train: "Welcome to organised chaos! This train will now run as booked calling at Bolton...Chorley...Preston."

To poor infrastucture investment - doing things on the cheap

Or just general malfunctioning.

Can someone put me right?

 

[175001]

Yesterdays problems was caused by multiple cable theft near Lostock Junction, that's due to some of the wonderful residents of this country.

 

[ainsworth74]

All of the above really, perhaps it varies from place to place but in some areas the main cause of signalling failures tends to be copper fairies nabbing the wire (I'm thinking around Leeds especially). In other areas it could well be the age of the signalling systems themselves. Then again it could be gremlins in the system and things just going wrong for no reason in particuar. Every failure for the most part will be different and so to its causes be different.

 

[EM2]

All sorts of reasons.

Rodents nibbling cables is a favourite
Lightning strike is not unknown
Lineside fire
Mechanical failure of points (that means a route can't be set through)
Sticking relay on a track circuit (so circuit shows as occupied)

With the last two, that means the protecting signal will be held at red.

 

[Old Timer]

There are several "failure" modes as far as signals are concerned.

Of true failures to the signal, only a lamp burning out or a fuse blowing are true failures.

In the remainder of the situations, the signal is working correctly but the inputs to the signalling controls are insufficient to allow the signal to indicate a proceed indication.

When a route is set, the interlocking carries out a variety of functions, which will broadly encompass the following very simplified (and not necessarily in the specific order) protocols :-

Route check to establish that the no part of the route is not in use for another route ;

Overlap check to confirm that overlap is not in use by another route ;

Aspect check to prove signal at exit of route is alight ;

Track circuit check to prove all required track circuits are showing unoccupied ;

Points free to be operated check - ie check that points are not in use by another route for example flanking protection, and that are not locked by IPS ;

The route is now free to be set.

The final check is that all points are locked, at which point the protecting signal will clear for the route.

Now as will be appreciated, there are sometimes tens of relays within this operation, and occasionally one can develop a fault, typically what is called a "high resistance fault", whereby there is a build up of material on the relay which is off too high a resistance for the current to pass through.

On the track a track circuit may show occupied when in fact it is clear, and obviously points may not go into detection. Again there are numerous relays in lineside cabinets which can develop faults.

 

[strange6]

Yesterdays problems was caused by multiple cable theft near Lostock Junction, that's due to some of the wonderful residents of this country.

I'm assuming you mean about the Bolton signalling problems. Was that cause by sheer vandalism or by cable theft???

 

[Dolive22]

OT, do you know if it would be difficult to use fibre optics as they're not worth much once nicked?

 

[IanPooleTrains]

Yesterdays problems was caused by multiple cable theft near Lostock Junction, that's due to some of the wonderful residents of this country.

They must be the same wonderful people that do that on The Chase Line and therefore meaning that if a train is microscopically late, they decide to terminate the train at Hednesford and not run down to Rugeley Town or Rugeley Trent Valley

 

[asylumxl]

Shame we can't electricute the thiefs. Make the exterior of the cable live, and have a sign saying by passing the sign they agree to being liable for their actions They'd be much easier to locate. Though i fear clearing the body may infact cause more delays.

 

[sprite]

They wear gloves incase of being zapped and because of smart water (they avoid this by burning the plastic off before weighing it in) .
The one problem I see with fibre optics is they cannot replace all the copper as they cannot carry the electricity to power the signals, point motors etc. Replacing data lines with fibre does works and reduces the copper out there to be lifted so its still a step forward.

 

[Dolive22]

I was thinking that cables with proper juice in them were safe and they only nicked ones carrying data with it's tiny voltages and wattage. But thinking about it, loads of the nicked cables are power rather than control. I'm obviously not at my best after midnight.

 

[sprite]

The word "wattage" makes me cringe, its power (Im a physics student, the same goes for "ampage, that should be current),The data cables may be relatively low voltage compared to the power lines, but without consulting the S&T staff I know I would geuss that they would still pacl a small punch as a higher voltage is needed due to the distances involved. No doubt though they doubt they would carry less current though, and current is the killer.

 

[EM2]

Even the power cables for signals and points are only 110V, which, although enough to give you a decent belt, is rarely fatal.

 

[Peter Mugridge]

I was thinking that cables with proper juice in them were safe and they only nicked ones carrying data with it's tiny voltages and wattage. But thinking about it, loads of the nicked cables are power rather than control. I'm obviously not at my best after midnight.

It's not unknown ( but rare ) for the 25kV overhead cables to get nicked.

I know how they do it without getting zapped, but I'm certainly not going to post it in case any miscreants are looking through these forums to try to get ideas.

 

[Ploughman]

To add to the list
There is also the degradation of the cable insulation.
There are some locations were you are banned from even touching the cables in case they fall apart.

 

[Hydro]

What causes signal failures in the UK?

Labour agencies packing IBJ's.


/cynic.

 

[the sniper]

Rodents nibbling cables is a favourite

Didn't this result in a fire and complete shut down of Birmingham New Street a couple of years ago? Or am I imaging that?

 

[ayrshire_voyager]

I see Glasgow Central has went down the tubes again today,absolute nightmare

 

[CarterUSM]

I see Glasgow Central has went down the tubes again today,absolute nightmare

Nothing to do with signals though, trespass incident, and I think they have been hurt or worse apparently.

 

[Old Timer]

OT, do you know if it would be difficult to use fibre optics as they're not worth much once nicked?

Yes and no.

Digital signals can be carried by Fibre optic cables, as can telephone signals.

Many years ago BR commenced Project Mercury, which was the installation of fibre optic cabling along the railway line, so that modern telecomms system could be used. Mercury will ring bells (if you pardon the pun) with the former Mercury mobile phone network

Signalling controls however generally require an electric current, which means they have to be copper or a copper combination. In addition the lineside power cables are still required to power up the location cases and the trackside signalling equipment. These carry 650v.

There will always be a need for trackside power so some form of power supply cabling will be required.

Where I am now, the Railway actually operates its own HV power electricity distribution network, which runs on a HV pylon route, with connections into the relay rooms.

Signalling command controls are bounced from the Control Centre via geostationary satellites to the various relay rooms which are equipped with satellite receiver dishes. This cuts down on lineside route to a large percentage.

Any trackside cable route however will always suffer from the eternal rodent problem. Cable routes are like a motorway network to a rat or mouse (the two dont live alongside each other, so where you have one you dont have the other), and in addition they provide a safe, dry, and warm place in which to stay. The cable steel sheaths are perfect for the rodent that just needs a constant hard dubstance on which to sharpen and wear down its teeth. Left alone a rat's teeth would eventually prevent it eating, which is why they nibble so much

 

[ayrshire_voyager]

Nothing to do with signals though, trespass incident, and I think they have been hurt or worse apparently.

I know the engineering works were over-running.......but

 

[Via Bank]

Stupid question: what if one of a signal's bulbs blows? Even if they're not old-fashioned filament lamps, they'll wear out eventually.

 

[the sniper]

Stupid question: what if one of a signal's bulbs blows? Even if they're not old-fashioned filament lamps, they'll wear out eventually.

Do you mean, what happens if no aspect is shown to the driver at a signal?

If a driver sees a blank signal, it has to be treated as though it's displaying a danger (aka red) aspect. Thus, they'll stop and then contact the signaller.

 

[ralphchadkirk]

Stupid question: what if one of a signal's bulbs blows? Even if they're not old-fashioned filament lamps, they'll wear out eventually.

Then the auxiliary filament takes over and a warning signal is displayed to the signalman/tech staff.
--- old post above --- --- new post below ---

Do you mean, what happens if no aspect is shown to the driver at a signal?

If a driver sees a blank signal, it has to be treated as though it's displaying a danger (aka red) aspect. Thus, they'll stop and then contact the signaller.

The signal is treated as displaying it's most restrictive aspect; not necessarily red.

 

[moggie]

OT that's interesting. Of course in the UK those systems utilising remote relay rooms will generally empoy a TDM system which of course requires minimal cabling. The principle cable demand is the connection from interlocking to the lineside equipments locs (and locs to lieside signalling equipment). Use of Fibre Optic to connect the control point to the interlocking for the non-vital signalling commands and indications is possible and in fact is present at certain installations. However, as you rightly point out interface bewteen the interlocking and lineside equipment generally requires to drive a relay or monitor a voltage. The main problems are the number of locations along the lineside that a connection with the FO cable would be required. The number of signalling functions that would need to be connected at each location (more than the number of telephones!) and the predictability of failure in the vital interface equipment between the FO cable and signalling equipment that would be necessary to ensure safety integrity. No doubt all possible in theory but prohibitively expensive. Of course that's what solid state / computer based systems largely resolved.
--- old post above --- --- new post below ---
Agree - that's what the driver / signaller will do. The signalling system will also revert the signal on the approach to the failed signal (main) to it's most restrictive aspect if both filaments have failed under a TCB block system. There are some variations to this rule on older signalling systems but this would be the general rule.

 

[Old Timer]

Moggie,

Here is an example, note the satellite dish above the U-Boats. The Driver (who is now a friend) is just winding them up to full power having relieved the inwards crew, however the heat prevents a full appreciation of the exhaust pattern.

 

[moggie]

Looks like the local gang who presumably reside in the adjacent coach have rigged it up to Sky already!

 

[DaveNewcastle]

Re: replacing multi-strand wire cables with multiplexed fibre-optic cables.
These, too, are cut and taken off site (leading to the same disruption as the loss of hard-wired lineside conductors).
Presumably the culprits hope that the fibre-optic bundles contain metals and only discover their error after cutting and removing the bundles.

 

[Old Timer]

Looks like the local gang who presumably reside in the adjacent coach have rigged it up to Sky already!

It does but it isn't.

 

[JoeGJ1984]

Do you mean, what happens if no aspect is shown to the driver at a signal?

If a driver sees a blank signal, it has to be treated as though it's displaying a danger (aka red) aspect. Thus, they'll stop and then contact the signaller.

What happens if travelling at high speed and a blank signal is shown due to a bulb failing? Say that all the signals in the area (including the one with a blown-out bulb) are 4-aspect signals, the previous signal is green (thus giving no warning or need to slow down), then the driver sees a blank signal? I think he would not be able to stop in time.

Would he then slam on the emergency brakes? What about the AWS (i.e. if the associated AWS magnet gives a 'clear' indication, could the driver assume the signal is green?)