How Do Signallers Know Where Trains Are? A Guide to Railway Train Detection Systems
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- Опубликовано: 26 июн 2024
- 🚆 Ever wondered how signallers keep track of trains on the railway?
🛤️ In this video, we dive into the fascinating world of railway train detection. From bustling city networks to remote tracks, discover how signallers ensure every train’s location is known.
✔️ Learn about fixed block signalling systems and the two main train detection methods: Track Circuits and Axle Counters. Understand the pros and cons of each system, how they prevent collisions, and ensure safe train passage.
💡 Explore the technical details of track circuits, axle counters, and how modern systems like ERTMS work.
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Video Chapter's:
00:00 - Intro
00:47 - Train detection
01:09 - Fixed Block Signalling
02:23 - Track Circuits
03:23 - Track Circuits - Advantages
02:59 - Track Circuits - Disadvantages
06:54 - Jointless Track Circuits
07:39 - Axle Counters
08:08 - Axle Counters - Advantages
08:41 - Axle Counters - Disadvantages
09:38 - Summary 
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Just a recreational enthusiast here: love the nitty-gritty geeky stuff. Thank you.
Glad you enjoyed it!
As A qualfied signalman on a preserved line I found this interesting although I already knew how track circuits worked. I very nice and simple explanation.
Hi Terry, thank you for the feedback, I really appreciate it. Very glad you found it an interesting video
Decent overview, some nits to pick on the S&T side of it; the way you worded the reference to moving blocks makes it sound like they're exclusive to ERTMS, though they're just a general signalling concept. Tokens aren't really detection, since it relies on compliance by the driver. Also not sure that it'd be *audio* frequencies.
Also realise I'm incredibly late in saying this, but it's nice to hear this in your own voice, I remember the first video I came across a while ago was one of the TTS ones.
Thank you for the feedback! Glad the move to voice has been an improvement
Track circuit should also be used together with signal system. For example Chinese version of ETCS L1, the CTCS 2, use fixed balise to transmit line/speed info. But signal status is transmitted via track circuit, due to China railway used track circuit instead of axle counter. So signal status is continuously transmitted even in ETCS L1 equivalent mode. And enable ATO even in ETCS L1/CTCS 2 mode. No need for 40 kph exit window and driver observation.
What would be the factors to take into account if a track gauge could be chosen freely (without backward compatibility requirements)? What gauge would you chose for a heavy haul freight line (say, iron ore with high axle load)? Can you make a video on this?
Now that is an interesting question. I was looking to do a video on gauges around the world, so maybe it can tie into that
It seems axle counters have some operational issues but no safety issues as a track circuit could cause. I think this is the reason why axle counters become more and more popular.
Not all systems behave like explained in the video. There are axle counting systems where reseting the axle counter frees the block. Which can be deadly if there is in fact a train on the block.
Also a faulty axle counter in the beginning of a block won't make the section occupied. So the system needs to detect faulty axle counters.. Which seems to work pretty well so far. But in my humble opinion it's an accident waiting to happen.
@@alexanderohman1707 In theory of course. But in practical terms the UK Network Rail signalling SYSTEM makes such an event extremely unlikely. The application Safety Case for each new installation demands so.
In UK practice in areas where Axle Counters are the predominant form of Train Detection, if a train leaves a section of line occupied behind, the signaller will alerted by their control and display equipment of and out of sequence occupation and clearance of the track section(s) as the train proceeds.
Safeguard 1: Before attempting to Reset the affected Axle Counter section(s) left occupied, the signaller must stop and contact the last train to check the train remains complete - i.e. to ensure it has not become divided. In all likelihood such an event would already have caused an out of course brake application alerting the driver to the issue and consequent actions required.
Safeguard 2: Assuming no obvious reason on this train is identifiable the signaller can attempt a Conditional Reset of the affected section(s). However, the signalling SYSTEM will prevent a remote (i.e. signaller) Reset unless there has been a partial count out of the affected section registered by the Axle Counter evaluator under 'normal working' arrangements. This is the 'conditional' feature in play. The majority of 'miscounts' involve a count OUT which is unequal to the count IN so the Conditional Reset attempt will prove successful.
Safeguard 3: However, a further safeguard is then imposed by the signalling SYSTEM (interlocking) which holds every signal protecting the affected section at red. This is known as Aspect Restriction. The Track Section shows CLEAR to the interlocking allowing routes to be SET but protecting signals cannot show a proceed aspect.
To remove Aspect Restriction from the signal route a train must pass this signal and travel through the affected section under signallers caution and check for any obstruction of the line. A standard Rule BooK procedure where the driver is advised of the circumstance, authorised to pass signal at red and inspect the line. After passing through the affected section the driver must report the line status back to the signaller. The action of the train passing through the section automatically removes the restriction placed on the signal for the next train. If the driver reports an obstruction then other standard Rule Book line protection processes are invoked. If the affected section is through S&C then a single train movement through each axis of the section MAY be needed to remove ALL Aspect Restrictions.
Safeguard 4: If unusually a remote Reset is prevented the only way a Rest can be achieved is to send the Technician to the site to perform a manual reset at the evaluator. Again, standard Rule Book procedures to ensure the section of line is clear must be followed by both signaller and technician before Reset is undertaken.
Safeguard 5 - Possession handback: If it is known an Axle Counter may be disturbed during rail movements, for example by wheeled vehicles which are known not operate the counting head effectively and / or during Engineering Possessions then a pre-planned invocation of the EPR control feature by the signaller will occur at the start of possession, before any axle counter becomes disturbed. This may be invoked across one or many sections at a time. When EPR is present and Reset of axle counter section(s) is attempted the Evaluator will not enforce the partial 'count out' feature. Neither will the interlocking invoke Aspect Restriction. In such instances the handback of the work site and the process which ensures all rail plant and personnel are off track and accounted for also includes a manual 'sweep' of the affected section of line before handback to traffic and normal working is resumed.
Safeguard 6: Systems in use in the UK generally perform to SIL4 (the highest) - equivalent to that of signalling Interlocking equipment. This renders the risk of equipment malfunction leading to a false Reset as negligible.
In the UK it is now 21 years since the first application of Axle Counters as the principal method of train detection was implemented (at Stoke on Trent SCC). Many have followed. I know of no serious event due to erroneous Reset which has compromised the safety of train running.
Bit of a long winded response but I consider it important to dispel myths around how 'easy' a false reset by a signaller leading to a catastrophic event actually is. I hope this explains it
The benefit a track circuit has that an axle counter doesn't is continuous detection, and this does have some safety implications. That said, I don't think it's straightforward to say that one or the other is more or less safe, it's going to come down to the actual installations and the maintenance and operating procedures around them.
Another advantage of the track circuit is that you can artificially create a short circuit that protect the workers in a track works area
It is indeed Gary, I had this down as a disadvantage of axle counters but missed it as a TC advantage
Could you do a video about rolling blocks and ERTMS?
Another issue with track circuits is specific rolling stock not breaking the circuit. This problem occurred in Ireland.
I didn’t realise this happened, do you have any more info on it?
@@thepwayengineerThis was c.25 years ago. it was kept very hush hush. Specific railcars on Irish Rail were not trusted to operate track circuits reliably. Many unmanned signal cabins became re-manned as a human was required to verify that a train had actually passed out of section. I cynically assume that this is what lead Irish Rail to go all in in axle counters.
@@ewanduffy This happened Downunder in Victoria Australia with the Sprinter Railcars built in the early 90s (similar in appearance to British Class 153). Several remedies were tested but instructions still require single units not to operate in certain areas.
The audio version of track circuits sounds really interesting, so a video on that might be quite informative. Also, if you could explain how axel counters count axels exactly, that would be good too. What about Talgo trains that don't have a single axel between wheels, how do they work with these systems? Thanks for the video.
Not sure on the exact method of detection, though afaik it's magnetic in some way, we're told to keep ourselves/tools >300mm away from axle counter heads to prevent false detection. They're fitted pretty close to the running rails, so I'd think that it'd probably not be an issue for Talgo trains, though I might be wrong.
An axle counter is a proximity detector which gives a pulse each time the magnetic field around it I’d
S disturbed by a wheel. A computer counts the pulses and stores the information in its memory. When the next axle counter counts pulses it subtracts them from the first memory and adds them to the next. Provided that the same number of pulses equals zero then it shows the track to be clear.
Re Talgo wheels, with track circuits the wheels are cross bonded electrically so they do interrupt the track circuit. With axle counters the count is the same.. To overcome the possible “loss” of a train while using sanders most countries instruct drivers to stop with sand and then move forward a coach length onto unsanded track.
With the trackcircuit, the train shortcuts the electric current, preventing it from activating the relais. But at the same time the train shortcuts the power source. Now you can not simply shortcut the power source. So how do they do it?
Adding a certain kind of resistance between the power source and the track itself. So the unoccupied track circuit is like power source, resistance, track, relay, track, power source. While occupied the current cuts the relay short but still has the resistor (in most cases a kind of a coil as far as I know) in series with the power source.
@@DonkenAndToivolaRR That could be it. Thanks! I know that here in the Netherlands we have those trackcircuits (and on some branche lines axle counters), and these days they use electronics systems instead of the old relais systems.
Presumably track circuits aren't compatible with electrified railway lines. Or is there some clever way that they still work?
The rail network I work on, New York City Transit, the track circuits are low voltage AC, whereas the traction power is DC at 600 volts.
It’s much like the filters that get attached to older copper wire phone lines to filter out the internet signals, you just need to filter the DC current from the AC current.
They're compatible, fairly common for electrified track to be track circuited here
Although compatibility with electric traction is not mentioned in this short presentation, track circuits have been used with both third rail d.c. and overhead 25 kV electric. In the third rail system, with heavy current at around 750V d.c. , most of the time both rails are used for traction current, and track circuits that use frequencies that are immune to the traction current, and there are also “traction bonds” to route the traction current past the track circuit bonds, but not the track circuit current.
Much of the 25 kV lines had only one rail for traction return, with the other being the track circuit rail. This was practical as the current is a lot lower at 25 kV. Suitable relays that are immune to the traction system were used. The rail used for each swapped over at each track circuit joint, with a lot of cross bonding for traction through the whole system. The overall interface between electric traction, signalling, and permanent way, is a topic of it’s own.
A relatively small amount of the 25 kV fitted lines did use jointless track circuits that were compatible with a.c. traction, with both rails being used for both functions. ISTR the trade term was TI-21M, originally used between London Paddington & Heathrow airport. Don’t know if that’s still in service, or replaced by axle counters though.
Your train shorted out the battery and the battery now caught on fire
Won't acknowledge pressing Like. So you know.
Thank you!