Track circuits at level crossings?

[BigDog]

How long is the usual length of a track circuit on the approach to a level crossing, I'm guessing the last IBJ is hundreds of meters before the level crossing?

 

[Elecman]

May not be track circuit operated could be treadle operated but the actuating methods will be a suitable distance before the level crossing to give the necesssry operating time for the barriers to lower and signals to clear

 

[BigDog]

May not be track circuit operated could be treadle operated but the actuating methods will be a suitable distance before the level crossing to give the necesssry operating time for the barriers to lower and signals to clear

Treadles are only in axle counter areas, no?

 

[MarkyT]

May not be track circuit operated could be treadle operated but the actuating methods will be a suitable distance before the level crossing to give the necesssry operating time for the barriers to lower and signals to clear

For automatic highway crossings, a combination of track circuits and treadles is used at the so called 'strike-in point', which is positioned to ensure the minimum required road warning time is always given even for the fastest trains. More complex arrangements are implemented where there's a signal within the strike in distance to avoid the crossing being closed to road traffic for extended periods beyond a maximum stated in the legal crossing order, if some trains stop at a station in this area for example - the fear being that otherwise road users may assume the crossing has failed and attempt to weave around the half barriers. Treadles are heavily damped momentary switches with an arm attached actuated by the flange of a passing wheel, but approved inductive sensor equivalents are also available today, and axle counter systems, also using inductive flange sensors, can be used in lieu of traditional track circuits. There are some crossings in East Anglia that use a special kind of track circuit strike-in system called a predictor. This uses the change in electrical characteristics over time of the approach track circuit to determine the speed of an oncoming train and vary the physical point at which the road warnings start so the warning time is less variable. These have been used in the USA for many decades, and the East Anglian equipment was supplied by an American manufacturer.

 

[Llanigraham]

Treadles are only in axle counter areas, no?

No. Treadles can be anywhere.

 

[High Dyke]

Treadles are only in axle counter areas, no?

Following on from MarkyT's post. AHB crossings are not usually linked to the signals, like a traditional crossing would be. I am used to working locations that have these, and most work by treadles. Where a station platform is close to the crossing, the supervising signal box will have a stopping/non-stopping facility. This changes the approach timings.

 

[BigDog]

No. Treadles can be anywhere.

So, is there any way to tell? It would be a great benefit for people who use a track trolley regularly.

 

[12LDA28C]

So, is there any way to tell? It would be a great benefit for people who use a track trolley regularly.

What exactly are you asking here? Would a track trolley not be used within a possession or at least a line block? Red zone working is not allowed any more so I don't see how you'd be using a trolley whilst trains are running.

 

[BigDog]

What exactly are you asking here? Would a track trolley not be used within a possession or at least a line block? Red zone working is not allowed any more so I don't see how you'd be using a trolley whilst trains are running.

Exactly what I asked, so in theory if you placed a track trolley beyond the treadle you could push it anywhere in that section without triggering the level crossing.

 

[alxndr]

Treadles are only in axle counter areas, no?

Treadles are more likely to be found on track circuited area than axle counter areas. Treadles are used in track circuited areas around crossings to remove the risk of a track circuit failing to detect a train. This is less of a risk with axle counters as they don’t suffer the same issues with rusty rails.

So, is there any way to tell? It would be a great benefit for people who use a track trolley regularly.

If you work on the railway then it sounds like you need a discussion with the local S&T department to understand their signalling arrangements and what you can/can’t do without affecting the crossing.

Exactly what I asked, so in theory if you placed a track trolley beyond the treadle you could push it anywhere in that section without triggering the level crossing.

If it was an axle counter area, then theoretically yes. In a track circuit area no. In reality you must obey the rules in Handbook 10:

2.5 Level crossings
You must not allow the trolley to:

• pass over a manually-controlled level crossing unless the barriers are lowered or the gates are closed to road traffic and you are sure it is safe to do so
• come within the controls of an ABCL or AOCL
• come within the controls of an AHBC unless it is under local control
• pass over an AHBC unless it is under local control and the attendant displays a green handsignal
• pass over a level crossing which has red and green warning lights unless you have made sure it is safe to do so
• pass over a CCTV, OD or RC crossing without the signaller's authority.

 

[swt_passenger]

Treadles are more likely to be found on track circuited area than axle counter areas. Treadles are used in track bc or cities areas around crossings to remove the risk of a track circuit failing to detect a train.

Is that what you intended to write?

 

[endofthetunnel]

If you’re putting a trolley on the railway then this should be discussed with the signaller beforehand - by you or your COSS, during the process of taking the line blockage or possession that you are presumably protected by. If you’re using a trolley regularly I guess you already do this. The usual solution for a trolley being close to a crossing is to take it on local control.

Every crossing is different and there are no blanket rules as to how close you can be, there are also other things to consider perhaps (things like miniature red/green crossings, interlocking issues, sets of points) and its odd to be asking this on a forum rather than at work.

 

[BigDog]

It's just a general question that I'm asking. Of course we acknowledge the signaller if we are placing a trolley on the track under a line blockage, but it would be handy to know how close you can push a trolley without triggering a level crossing. We just ensure we don't push the trolley over the IBJ near the crossing.

 

[endofthetunnel]

Fair enough!
The closest IBJ is a good marker but the exact length obviously varies. Treadles should be easy to avoid, just be aware they exist both sides of the crossing, sometimes for wrong direction moves and usually for proving the train has fully passed over.

For signal protected crossings like CCTV or OD, any TC between the signal and crossing normally starts the lights and sirens immediately as it assumes a train has SPADed, even if you’re not on it.
For some automatic crossings the track circuits aren’t relevant at all so you really do need local knowledge for each crossing that most signallers would be happy to talk you through.

 

[alxndr]

Is that what you intended to write?

No, was intended to be "track circuitted", editted now.

It's just a general question that I'm asking. Of course we acknowledge the signaller if we are placing a trolley on the track under a line blockage, but it would be handy to know how close you can push a trolley without triggering a level crossing. We just ensure we don't push the trolley over the IBJ near the crossing.

There are too many variables (crossing type, train detection type, linespeed, bi-directional working, etc) to give a generalised answer.
If in doubt ask and/or assume that you will affect the crossing.

 

[MarkyT]

Modern full barrier MCB crossings that are interlocked with signals and have supervision by a local attendant, remote control and CCTV from a distant signalbox or Obstacle Detection have an auto lower feature initiated by track circuits. Because of the signal interlocking, these TCs don't need reinforcing with treadles - worst case scenario is the crossing doesn't activate so the train comes to a controlled stand at the red before the crossing; inconvenient but not unsafe. The initiating point for auto lower is much further out from the crossing than the case with half barrier crossings as the idea is to give the train driver unrestricted aspects over the crossing so the road warnings must start long before the train has seen a cautionary aspect on approach. MCB crossings are usually equipped with treadles around the crossing itself for 'strike out' purposes, and there are also some installations with treadles on final approach to a signal immediately before a crossing for SPAD prediction; if the train is supposed to be stopping with the road still open to traffic, but the equipment determines it won't actually pull up successfully before the red, the road warnings and barrier lowering are started immediately automatically.

Auto lower can be switched off by the signaller if desired at MCBs but I wouldn't bank on that occuring every time routinely in a possession.

There's a new generation of self contained warning systems for smaller private and footpath crossings with red/green warning lights and sometimes gate locks. These are often designed to be entirely separate from the wider signalling system and are initiated by dedicated treadles or equivalent inductive sensors on approach.

 

[LAX54]

Treadles are only in axle counter areas, no?

Most, if not all AHB's will be treadle operated, some in conjunction with track circuits, when AHB's were track operated only, if we had a train that was not guaranteed to operater tracks either had to be cautioned, or in some cases the barriers manned, the addition of treadles stopped all that.

 

[RailwayRookie]

Modern full barrier MCB crossings that are interlocked with signals and have supervision by a local attendant, remote control and CCTV from a distant signalbox or Obstacle Detection have an auto lower feature initiated by track circuits. Because of the signal interlocking, these TCs don't need reinforcing with treadles - worst case scenario is the crossing doesn't activate so the train comes to a controlled stand at the red before the crossing; inconvenient but not unsafe. The initiating point for auto lower is much further out from the crossing than the case with half barrier crossings as the idea is to give the train driver unrestricted aspects over the crossing so the road warnings must start long before the train has seen a cautionary aspect on approach. MCB crossings are usually equipped with treadles around the crossing itself for 'strike out' purposes, and there are also some installations with treadles on final approach to a signal immediately before a crossing for SPAD prediction; if the train is supposed to be stopping with the road still open to traffic, but the equipment determines it won't actually pull up successfully before the red, the road warnings and barrier lowering are started immediately automatically.

Auto lower can be switched off by the signaller if desired at MCBs but I wouldn't bank on that occuring every time routinely in a possession.

There's a new generation of self contained warning systems for smaller private and footpath crossings with red/green warning lights and sometimes gate locks. These are often designed to be entirely separate from the wider signalling system and are initiated by dedicated treadles or equivalent inductive sensors on approach.

A very consise explanation but also of note is that not all MCBs have auto raise or auto lower. They can have neither, either or both.

And with SPAD prediction, the light sequence skips the Amber aspect and goes straight to double flashing reds but the barrier lowering sequence should not start automatically because of the trap risk. It is usually the case that If the SPAD predictor is triggered the crossing will need to be 'cycled' in order to stop the lights and wailers.

 

[MarkyT]

A very consise explanation but also of note is that not all MCBs have auto raise or auto lower. They can have neither, either or both.

That's very true. It's why I wrote modern crossings because it has become increasingly common in renewed installations but even now there will be locations not suitable, especially the auto lower feature, particularly when a crossing is very busy with pedestrians and lowering barriers needs to be done very carefully under human supervision. Auto raise has been more common for a long time but still there might be locations not suitable. Having both is a prerequisite for OD-equipped crossings or they wouldn't be able to operate completely automatically normally without any intervention by an attendant/signaller, which is their primary raison d'être.

== Doublepost prevention - post automatically merged: 12 Oct 2024 ==

I should add that raising barriers can also be a risk at crossings busy with lots of waiting pedestrians. There have been cases where dog leads, even children have been temporarily secured to the barrier by people waiting that have taken a sudden vertical excursion when the booms rise.

 

[John Webb]

A sudden thought concerning TCs in the vicinity of level crossings: in Winter and with any ice or snow on the road the road may be salted. Now salty water is a much better conductor than plain water. Does this ever cause any problems?

 

[Llanigraham]

A sudden thought concerning TCs in the vicinity of level crossings: in Winter and with any ice or snow on the road the road may be salted. Now salty water is a much better conductor than plain water. Does this ever cause any problems?

Yes it can cause a problem so generally I understand the instruction to gritter drivers is not to grit within a certain distance of the crossing, but of course that doesn't take into account the transfer of salt on vehicle tyres.

 

[MarkyT]

A sudden thought concerning TCs in the vicinity of level crossings: in Winter and with any ice or snow on the road the road may be salted. Now salty water is a much better conductor than plain water. Does this ever cause any problems?

Probably part of the reason current standard designs include a separate short track circuit over the road surface. That is proved occupied then clear in the strike-out sequence, along with some local treadles being operated then normalised, before barriers can rise but alone will not initiate a new warning if it goes occupied unexpectedly. Metal wheeled traction engines, road rollers, tracked agricultural, construction and military vehicles can also occupy a track circuit crossing a road. Older crossings from the 1960s and 70s didn't include this separate TC so could be triggered by this scenario. Use of axle counters avoids these problems.

 

[BigDog]

I have noticed that in track circuit areas you can push a track trolley really close to a CCTV level crossing before requesting the signaller to lower them before you cross the road, I'm guessing they would not lower at all without the request.

 

[Taunton]

A sudden thought concerning TCs in the vicinity of level crossings: in Winter and with any ice or snow on the road the road may be salted. Now salty water is a much better conductor than plain water. Does this ever cause any problems?

Another issue at track circuited road crossings is excavators etc on (metal) caterpillar tracks going over, which can short across all sorts of combinations as they cross.

For some automatic crossings the track circuits aren’t relevant at all so you really do need local knowledge for each crossing that most signallers would be happy to talk you through.

I know I have written here before about the accident some years ago at Athelney crossing, but one of the issues there, from reading the RAIB report, was uncertainty among various levels of the signalling staff and management about how it exactly worked in irregular operations. So much for "local knowledge". It was a treadle-operated AHB, whose sequencing had been disrupted during overnight track works by a tamper running wrong line over the treadles. The accident train was the first one through next morning.

 

[BigDog]

Another issue at track circuited road crossings is excavators etc on (metal) caterpillar tracks going over, which can short across all sorts of combinations as they cross.



I know I have written here before about the accident some years ago at Athelney crossing, but one of the issues there, from reading the RAIB report, was uncertainty among various levels of the signalling staff and management about how it exactly worked in irregular operations. So much for "local knowledge". It was a treadle-operated AHB, whose sequencing had been disrupted during overnight track works by a tamper running wrong line over the treadles. The accident train was the first one through next morning.

Mate, I've never heard of that one, all excavators going on track should have rubber tracks and protection is placed over the rails, a metal tracked excavator would take chunks out of the rail.

 

[RailwayRookie]

Mate, I've never heard of that one, all excavators going on track should have rubber tracks and protection is placed over the rails, a metal tracked excavator would take chunks out of the rail.

I think they mean metal tracked excavators using the road, not working rail equipment.

There's nothing to stop Bob the builder rolling his 61 Tonne Komatsu over an AHB and shorting the track circuits.

 

[MarkyT]

I have noticed that in track circuit areas you can push a track trolley really close to a CCTV level crossing before requesting the signaller to lower them before you cross the road, I'm guessing they would not lower at all without the request.

In most cases I think you're right. Many modern CCTV crossings have the auto lower feature, but it's always selectable by the signaller so if they want a quiet night its a very good idea to switch it off if there are track machines or trolleys moving about out in a possession. Instructions may mandate that.

 

[Tomnick]

In most cases I think you're right. Many modern CCTV crossings have the auto lower feature, but is always selectable by the signaller so if they want a quiet night its a very good idea to switch it off if there are track machines or trolleys moving about out in a possession. Instructions may mandate that.

Do they need a route set over the crossing for the auto-lower to function?

 

[MarkyT]

Do they need a route set over the crossing for the auto-lower to function?

I'd say yes if they are controlled signals, but they might usually be left in auto-working mode. The 'strike in' can be several signal sections long but if a train is legitimately in this area, and slowing for any red before the crossing, that will not immediately initiate a warning sequence.

 

[Tomnick]

I'd say yes if they are controlled signals, but they might usually be left in auto-working mode. The 'strike in' can be several signal sections long but if a train is legitimately in this area, and slowing for any red before the crossing, that will not immediately initiate a warning sequence.

Thanks, I thought that'd be the case. If they're in a possession, they must be kept at danger, so shouldn't have a route set from them or left in auto, so this situation shouldn't arise?

Incidentally, do you know how the interlocking deals with this, in normal signalling? Ordinarily, a route set over the crossing would prevent the barriers raising after one's passed on the other road. Does auto-lower somehow inhibit this, instead putting it's own separate request into the interlocking?