Axle Counters vs Track Circuits

[MarkyT]

With the trend towards solid state everything and IP networks all over the place, would the endgame be to put IP connections to each counter and do all the evaluation in the solid state interlocking?

Additionally, in the GSM-R era I suppose theoretically you could dispense with all the data cables and just use the radio to talk to the trackside equipment.....

Decades ago, Alst(h)om had a variant of the SSI platform that could evaluate axle counting directly in the interlocking system via special trackside function modules and software. It was used in Belgium and relied on a faster optical datalink than the metallic pair cabling used on UK schemes. ISTR there was a proposal for a UK trial, but I don't know if it went forward or what the assessment was. As far as I'm aware there has been no use of the tech in UK schemes.

Some of the Siemens axle counters, although having separate processor-based evaluator units, can communicate directly with the same manufacturer's SIMIS series of processor-based interlockings via a serial data link rather than via voltage-free contacts used in typical UK SSI schemes.

ISTR the 'regional' variant of ETCS deployed on some rural Swedish lines uses the GSM-R train radio to carry commands and indications to and from clusters of trackside equipment at junctions, passing loops and sidings.

 

[TSG]

Something sticks in my mind that Bournemouth had a lot of issues with this.

Bournemouth had a lot of issues with a lot of things. Almost every ****ing thing actually.

IIRC Bournemouth was pretty much the pilot for axle counters in the UK, done under Railtrack. and was about as successful as you might expect it to have been.

As people have pointed out, axle counters were used in 'tricky' spots before this, but I think you are right. This is where they first tried to do the whole scheme with axle counters, not just some soggy tunnel. Ironically though, they decided they needed a few track circuits where RRVs on and off tracked, to speed up the hand back of possessions.

but what about re-starting the railway from a black-out?

For various reasons, including axle counters, security of supply is taken more seriously (for a busy railway anyway) these days. Apparatus case suites can have a mini UPS to keep the axle counters from losing their memory. The suite can be supplied by two different power cabinets. If a power cable fault is detected the two cabinets will reconfigure the supply so that they supply suites each side of the cable fault. Each of the power cabinets can have a UPS and multiple automatically switched supplies such as one or more railway substations, a local electricity board feed or a backup generator. With all that, you can lose the supply, but it isn't a common occurrence.

With the trend towards solid state everything and IP networks all over the place, would the endgame be to put IP connections to each counter and do all the evaluation in the solid state interlocking?

Additionally, in the GSM-R era I suppose theoretically you could dispense with all the data cables and just use the radio to talk to the trackside equipment.....

I don't think GSM-R has the bandwidth spare for doing that on a large scale. Since you need to run one or more power cables there, sticking a fibre or two in the route at the same time is not a deal breaker. Like MarkyT describes though, for the middle of nowhere radio and off grid supply is the future I guess.

SSITM is obsolete but CBI in general, yes. The latest generation of axle counters is a world away from the rubbish they put in at Bournemouth and, amongst many other tricks, it uses a track side IP network so the cabling/comms is a lot simpler. It does it's own evaluation, not the interlocking, but this has benefits. Where needed it can tell the interlocking not simply clear or occupied, but direction, excess speed (SPAD prediction), and which head has struck in (virtual interrupters and reduced infrastructure at siding exits)

So, axle counters don't detect broken rails, the debris of a collision on an adjacent line, trolleys left on the line, heads on a rail that is no longer in use or whatever? Axle counters get used because if you sit in an engineering risks meeting and you think that the mitigation for:

• broken rails
• collision with debris
• collision with engineering equipment or materials left after a possession
• signalling equipment not restored correctly after works

is 'let's hope the track circuit picks that up', you shouldn't be there. There are other more effective things that you should be doing to prevent the hazard in the first place (regardless of train detection choice) and axle counters add at least as many slices of Swiss cheese as they take away. Don't forget, by letting the track engineer decide where they want to put joints in the rail and not drilling holes in it all over the place you probably increase rail integrity anyway.

 

[edwin_m]

Decades ago, Alst(h)om had a variant of the SSI platform that could evaluate axle counting directly in the interlocking system via special trackside function modules and software. It was used in Belgium and relied on a faster optical datalink than the metallic pair cabling used on UK schemes. ISTR there was a proposal for a UK trial, but I don't know if it went forward or what the assessment was. As far as I'm aware there has been no use of the tech in UK schemes.

Someone I shared an office with in BR Research about 1989 was working on a SSI trackside module that would connect to an axle counter, along with the software to manage the counts within the interlocking.

 

[Pigeon]

Yes they do as there is a smaller gap between 16.67 and either 0 or 50Hz and impedance bonds struggle much more with separating low frequency AC from DC.

I've always found it slightly amazing that those things are practical at all. Any idea what the actual inductance is?

 

[Annetts key]

Don't forget, by letting the track engineer decide where they want to put joints in the rail and not drilling holes in it all over the place you probably increase rail integrity anyway.

Not sure about that statement. Yes, the reduction of fishplated joints due to axle counters is an advantage. But joint less track circuit types had already solved this problem in plain line.

And don’t forget, having to have IRJs was not originally a big problem when track circuits were introduced, as most track was jointed 60 foot at the time. So holes in the rail for fishplates was not specific to the use of track circuits originally.

And in complex S&C, you can’t always weld everything anyway. So there will have to be some fishplated joints.

The most common defect where there is a hole drilled in the rail, is at a hole for a fishplate. In the vast majority of cases, the root cause is poor maintenance of the ballast formation under the sleepers in this area. Some time ago, the railway started replacing four hole fishplates with longer six hole types to try to mitigate this problem.

The track maintenance department routinely uses ultrasonic testing to identify any invisible defects in the rail. This has to happen regardless of the train detection system.

Although there are axle counter heads that can be clamped onto the rail, that idea has been abandoned for the scheme in my area. Hence all axle counter heads require holes to be drilled in the rail, and are then bolted to the rail. The situation may be different with different makes/designs of axle counter equipment.

The bolt holes for axle counter heads are considerably bigger than the holes used to attach track circuit cables to the rail.

As I said earlier, there are advantages and disadvantages for track circuits AND axle counters.

 

[Falcon1200]

3) prone to failure in very wet conditions

- Sea wall environments for similar reasons to bridges above

The TCs on the sea wall at Saltcoats failed every time high tide coincided with a breeze, so much so that five years after retiring I still recall their numbers, TC 46 (Up) and 49 (Down). Thankfully these were replaced by axle counters some years ago.

 

[MarkyT]

The TCs on the sea wall at Saltcoats failed every time high tide coincided with a breeze, so much so that five years after retiring I still recall their numbers, TC 46 (Up) and 49 (Down). Thankfully these were replaced by axle counters some years ago.

Before Exeter resignalling in the mid-1980s, the Dawlish sea wall and adjoining tidal riverside sections were signalled using traditional Absolute Block methods between a series of signalboxes at Exminster, Dawlish Warren, Dawlish (usually switched out), and Teignmouth, with very few track circuits along the vulnerable parts. The new scheme provided continuous track circuiting (using numerous individual TI21 jointless sections) that immediately started to fail en masse at high tide with an easterly wind, closing the railway far more than the previous technology. Very quickly, operators and the design office had to come up with a special method of emergency long block working that could be switched in only by the panel supervisor, and bypassed most of the track circuits.

https://www.signallingnotices.org.uk/scans/127/wr31_small.jpg

This was an interim measure until a better axle counter solution was designed to replace all the track circuits. When introduced and then extended also along parts of the Exe and Teign estuaries, I think this became the largest and most complex axle counter installation in the UK until the Bournemouth Siemens scheme.

 

[Annetts key]

The new scheme provided continuous track circuiting (using numerous individual TI21 jointless sections) that immediately started to fail en masse at high tide with an easterly wind, closing the railway far more than the previous technology.

Should have used Western Region AC Quick Release (designed originally by Westinghouse Signals Ltd I believe and manufactured by BR(W) under license).

We could get these to work in some atrocious ballast conditions, at the expense of having to monitor the BR938 relay voltage during dry/sunny spells. Oh, and the BR938 had to be a “double coil” Westinghouse type (QT2 I think), not the lighter weight equivalent from other manufacturers.

 

[TSG]

Not sure about that statement. Yes, the reduction of fishplated joints due to axle counters is an advantage. But joint less track circuit types had already solved this problem in plain line.

And don’t forget, having to have IRJs was not originally a big problem when track circuits were introduced, as most track was jointed 60 foot at the time. So holes in the rail for fishplates was not specific to the use of track circuits originally.

And in complex S&C, you can’t always weld everything anyway. So there will have to be some fishplated joints.

The most common defect where there is a hole drilled in the rail, is at a hole for a fishplate. In the vast majority of cases, the root cause is poor maintenance of the ballast formation under the sleepers in this area. Some time ago, the railway started replacing four hole fishplates with longer six hole types to try to mitigate this problem.

The track maintenance department routinely uses ultrasonic testing to identify any invisible defects in the rail. This has to happen regardless of the train detection system.

Although there are axle counter heads that can be clamped onto the rail, that idea has been abandoned for the scheme in my area. Hence all axle counter heads require holes to be drilled in the rail, and are then bolted to the rail. The situation may be different with different makes/designs of axle counter equipment.

The bolt holes for axle counter heads are considerably bigger than the holes used to attach track circuit cables to the rail.

As I said earlier, there are advantages and disadvantages for track circuits AND axle counters.

The jointed track was replaced with CWR to simplify the system so we could keep it safer with less work. As you say, reducing joints is an advantage and track circuits usually still need joints in S&C. Not having IRJs allows the track engineer to to eliminate joints if they see fit or put them wherever they feel would be best from a track system point of view. It gets rid of a complex 3 way interface between track, signalling and electrification. As you say, rail breaks often happen around joints, where the type or position of the break (i.e. chunk off top of bolt hole or cracked between bonding around the joint/beyond the track lead) means a track circuit is not likely to detect it.

The situation is different with some other axle counters, as they have perfectly effective clamps which need no drilling.

10 years ago I think I would have agreed with you that its a finely balanced decision. Track circuits have improved in that time but so have axle counters. I know there are some not so good axle counters out there and some questionable architectural decisions. However, the good axle counters are better than the good tracks now. The operational side has matured now too. There will be niche applications for track circuits but it usually makes sense to go for axle counters now.

 

[Tim M]

Track circuits cannot be duplicated, or to put it another way they present a single point failure that will ‘stop the job’ until fixed. Axle counters present opportunities to keep trains on the move with duplication or linking between sections. E.G. for the latter situation, take three wheel sensors A - B - C. Normally A and B work together as do B and C but it’s also possible link A and C such that a miscount at B can be ignored. This can be expressed in the form of an additional Train Absence Detection Control Table used to construct the data in the Axle Counter evaluator.

Note I have even seen axle counters overlaid on track circuits to increase availability following a track circuit failure, ref. Hong Kong Eastern Harbour Crossing turnback headshunt, that was 1989.

 

[Efini92]

moderator note: split from

Transpennine Route Upgrade and Electrification updates

Well it was suggested in the Manchester - Liverpool Electrification thread that we have a seperate Transpennine thread. Now I know that Manchester - Stalybridge is actually part of the Northern Hub project , but to me, haulage bashing Peaks in the 1970s-1980s - Liverpool-Newcastle was classed as...

www.railforums.co.uk

the other way round. Axle counters generally better, and only in service in a big way in this country for the last 30 years or so.

I was quite surprised to learn that track circuits have been around for over 100 years.

 

[Annetts key]

Track circuits have improved in that time but so have axle counters. I know there are some not so good axle counters out there and some questionable architectural decisions. However, the good axle counters are better than the good tracks now. The operational side has matured now too. There will be niche applications for track circuits but it usually makes sense to go for axle counters now.

Joint less track circuits (called joint less because they don’t need IRJs) have been around since 1967.

The current EBI Track 200 / Digital TI21 can be remotely monitored and requires significantly less maintenance compared to earlier designs.

The AzLM, K type axle counters that have been installed in my area have not been as reliable as we expected. In electronics, there is a graph that depicts reliability vs. time. It’s called a bathtub curve. Basically the number of failures may be high to start with, reliability then improves. The curve hopefully flattens to a straight line for a long time. Then as equipment ages, the failure rate starts increasing.

But due to rather a lot of component failures, poor installation, and various other problems, it’s taken a long time to get out of the infant mortality/first part of the bathtub curve.

And if a axle counter head, or it’s electric junction box needs changing, that normally takes about one hour. No amount of the signaller trying resets will get around such a failure.

So I’m not at all sure that axle counters are always better.

Track circuits cannot be duplicated, or to put it another way they present a single point failure that will ‘stop the job’ until fixed. Axle counters present opportunities to keep trains on the move with duplication or linking between sections. E.G. for the latter situation, take three wheel sensors A - B - C. Normally A and B work together as do B and C but it’s also possible link A and C such that a miscount at B can be ignored. This can be expressed in the form of an additional Train Absence Detection Control Table used to construct the data in the Axle Counter evaluator.

Note I have even seen axle counters overlaid on track circuits to increase availability following a track circuit failure, ref. Hong Kong Eastern Harbour Crossing turnback headshunt, that was 1989.

Err, yes, it is possible to have more than one track circuit on the same section of track. There are also other cheaper methods of increasing track circuit reliability.

But the current railway practices in this country don’t call for duplication for track circuits or axle counters. So both suffer from various single point of failure faults.

And as I said earlier, loss of an axle counter evaluator system will result in multiple axle counters failing, which the signaller can’t do anything about.

Obviously, the failure rate in my area is not going to be representative everywhere.

I’m just making the point that it’s definitely not a simple answer.

I was quite surprised to learn that track circuits have been around for over 100 years.

Yes, the basic track circuit as we know it today dates from about 1872.

Basic battery fed DC track circuits using shelf type relays are still in use in some places.

 

[alxndr]

The current EBI Track 200 / Digital TI21 can be remotely monitored and requires significantly less maintenance compared to earlier designs.

AZLM K type axle counters need even less maintenance though.

The AzLM, K type axle counters that have been installed in my area have not been as reliable as we expected. In electronics, there is a graph that depicts reliability vs. time. It’s called a bathtub curve. Basically the number of failures may be high to start with, reliability then improves. The curve hopefully flattens to a straight line for a long time. Then as equipment ages, the failure rate starts increasing.

But due to rather a lot of component failures, poor installation, and various other problems, it’s taken a long time to get out of the infant mortality/first part of the bathtub curve.

If it's anything like our installation they will come through and out of the initial high failure phase, even if it seems like there's no end in sight at first! All the failures we have now generally don't point towards poor installation being the root cause (aside from the decision not to heat certain location cases, but that's tangental argument).

And if a axle counter head, or it’s electric junction box needs changing, that normally takes about one hour. No amount of the signaller trying resets will get around such a failure.

With favourable conditions/locations/teammates I think I've had it down to 30 minutes for a electronic junction box and 20 minutes for a pair of heads, but I'd agree on estimating an hour to be on the safe side.

So I’m not at all sure that axle counters are always better.

Not always, but they do have their plus sides. We have vastly more axle counters than we have track circuits and yet I think I've been to equal amounts of failures on each in the last two years.

Another upside to axle counters that I don't think had been mentioned yet is that you can install the same type of axle counter in most places (although there are some layouts that aren't suited for them). Having everything the same means that you only need the competencies, experience, and spares for one type of equipment, rather than for multiple different ones. At one point we needed to be prepared for Aster U type, EBItrack 200 (analogue and digital Rx varieties), DC tracks and BR Western Region Quick Release Tracks.

 

[Annetts key]

AZLM K type axle counters need even less maintenance though.

See SMS/PartC/TC16 SERVICE C.

With favourable conditions/locations/teammates I think I've had it down to 30 minutes for a electronic junction box and 20 minutes for a pair of heads, but I'd agree on estimating an hour to be on the safe side.

Yes, sometimes it can be done quicker. It depends on where it is, how easy it is to physically get to and work on it, a bit of luck with the calibration/set-up, and for heads, where the cables have been routed (it’s particularly time consuming if they cross one or more lines, or go under a SCT route).

Not always, but they do have their plus sides. We have vastly more axle counters than we have track circuits and yet I think I've been to equal amounts of failures on each in the last two years.

Before renewals, we had far in excess of 1000 track circuits. Apart from the usual suspects, the vast majority very rarely failed. So far, the same cannot be said of axle counters. Even though some are now four years old.

Another upside to axle counters that I don't think had been mentioned yet is that you can install the same type of axle counter in most places (although there are some layouts that aren't suited for them). Having everything the same means that you only need the competencies, experience, and spares for one type of equipment, rather than for multiple different ones. At one point we needed to be prepared for Aster U type, EBItrack 200 (analogue and digital Rx varieties), DC tracks and BR Western Region Quick Release Tracks.

Maybe, but even the AzLM equipment (at least for the evaluator), we have two different incompatible types! Yes the serial and parallel cards are the same, but the CPU cards are different.

And we still have various types of track circuits.

Before renewals, we had:

• Aster U type / SF15
• Analogue TI21 (TX and RX) including some TI21/SF15 hybrid tracks
• Digital EBI Track 200 / TI21 (the current type)
• Primary cell DC low voltage track circuits (with shelf type relays)
• Secondary cell DC low voltage track circuits (with shelf type relays)
• Secondary cell DC medium voltage track circuits (with Q type relays)
• DC (transformer/rectifier) track circuits (either shelf type or Q type relays)
• DC (AC immune) BR904 or BR867 with BR 939A Q type relays
• BR Western Region Quick Release Tracks using shelf type relays (blue TRJ)
• BR Western Region Quick Release Tracks using Q type relays (yellow TRJ)
• BR Western Region Quick Release Tracks using Q type relays (white TRJ) (DC immune)
• Overlay track circuits
• The older non-computer based axle counters

But apart from the ASTER U/SF15 and EBI/TI 21 types, it was very uncommon to have to change any of the feed sets / resistors / TRJs. So having the different types was not really a problem.

We still have:

• Primary cell DC low voltage track circuits (with shelf type relays)
• Secondary cell DC low voltage track circuits (with shelf type relays)
• Secondary cell DC medium voltage track circuits (with Q type relays)
• DC (transformer/rectifier) track circuits (Q type relays)
• DC (AC immune) BR904 or BR867 with BR 939A Q type relays

Plus provide fault cover for

• Digital EBI Track 200 / TI21 (the current type)
• BR Western Region Quick Release Tracks using Q type relays (yellow TRJ)

So the widespread use of axle counter has not made that much difference in terms of spares.

 

[alxndr]

See SMS/PartC/TC16 SERVICE C.

I'll concede there, I'd not read that part as we don't have any remote monitoring on ours. There's not much difference between that and AX15, except that you do have to show up to the evaluator once a year there.

Maybe, but even the AzLM equipment (at least for the evaluator), we have two different incompatible types! Yes the serial and parallel cards are the same, but the CPU cards are different.

And we still have various types of track circuits.

...

So the widespread use of axle counter has not made that much difference in terms of spares.

I can see your problem there as you still have a fair mix. It has made a huge difference for us as we've almost wholly gone to axle counters, and aside from the electronic junction box and the rail contacts the spares are far smaller, which means we can carry more with us. Before we'd get a please explain if we didn't have spares on us for Asters or TI21s, but there's only so much you can put on a van at any one time, and it would be sod's law that you'd have everything bar the right frequency when you needed it.

 

[Annetts key]

To be fair, the SMS/PartC/TC16 SERVICE C is still officially only a trial at the moment.

Our area is a mix of 1970s (incorporating some earlier existing equipment), 1987/8 vintage, 1992/1993 vintage and 2016 to 2021 equipment. This is because the renewal scheme did not cover the whole area.

Before we'd get a please explain if we didn't have spares on us for Asters or TI21s, but there's only so much you can put on a van at any one time, and it would be sod's law that you'd have everything bar the right frequency when you needed it.

Never had a please explain for that

We did once have a new (analogue) TI21 that kept failing, but would self right long before we got on site. Someone in management (not someone who knew much about S&T) wanted us to just change everything. But this was a three section TI21, so that’s 3 x TX, 3 x RX, 8 x TU, 16 track leads etc. I declined on the basis that this was not practical (not enough spares or time)… But did not get a please explain.