Track noise

[Equinox]

Hi guys

Just been having a discussion with someone about 'that' noise the rail track makes shortly before a speeding train passes.

The noise I am talking about is a high pitch 'pinging ' sound which seems to resonate/bounce quickly along a section of track before a train speeds past.
I always assumed it was the sound of the power to the third rail being 'switched on' before the arrival of the train? But obviously I could be very wrong as my knowledge of railway engineering is poor. It doesn't seem like a vibration resonance from the train wheels, as it seems to start too suddenly.

Does this noise have an official 'name'? Or at least what would I call it to google, as I can't seem to find anything on it! I wanted to get hold of a recording of it.... But don't know what to type in other than 'train track electric pingy noise thing'... Which surprisingly doesn't return many results lol
Thanks!

 

[najaB]

I always assumed it was the sound of the power to the third rail being 'switched on' before the arrival of the train?

It definitely isn't since you get exactly the same sound in areas with overhead electrification and in non-electrified areas.

 

[Equinox]

I guess seeing as I only ever use southwest trains, all my experience of it comes from stations which have a third rail (hence my obviously wrong assumption!)

 

[Class172]

The effect leading to the sound comes from the running rails as opposed to the 3rd rail, since I have heard it at many locations. I would assume it derives from some sort of resonance vibration that propagate along the running rails due to the train.

At slower speeds, more noticeable is a sort of 'warbling woosh' (the only way I can describe it) as a train approaches; it can be heard a good while before the train arrives.

 

[Equinox]

Just seems strange that it starts immediately with a loud 'Ping' and then seems to bounce up and down getting quieter. You would think resonance from the wheels would slowly get louder and louder as the train approaches?

 

[Class172]

My theory would work for the second noise I mentioned, which does get louder, but I'd agree, it doesn't really work for the ping.

Perhaps it is caused as the train passes onto a new section of track, with the train passing onto it much akin to hitting a tuning fork. This could then cause sound to bounce down the rails?

 

[najaB]

Just seems strange that it starts immediately with a loud 'Ping' and then seems to bounce up and down getting quieter. You would think resonance from the wheels would slowly get louder and louder as the train approaches?

As a guess, the 'ping' is when the train crosses an expansion joint in continuous rail.

 

[Equinox]

That would certainly make sense ... Then it does lead to the question... Why that particular piece of track? As there is numerous sections in-between where the train is, and where the station is when the noise starts? As mention above it can be a long way off when the noise starts. If all track is connected similarly then why would that particular section of track cause it... But not the one before, or the one before that etc? As I said my knowledge is poor, so maybe there are actual gaps where the track is not actually physically connected in anyway?
Sorry for being a pain.. Things like this just niggle at me and annoy me if I don't understand them!! =D

 

[swt_passenger]

I always assumed it was the sound of the power to the third rail being 'switched on' before the arrival of the train?

I'll just highlight that that innocent misconception can lead to something of a safety issue. The third rail is always live. Real life trains do not work like simple model railways...

 

[najaB]

... so maybe there are actual gaps where the track is not actually physically connected in anyway?

Continuous-welded rail has to have have expansion gaps every few hundred meters, if it didn't then it would buckle in hot weather (well, more than it does already). I'm not sure how long the sections are, but it makes sense that vibrations would be attenuated by the gaps.

 

[Equinox]

I just had a read about expansion joints and think I understand now.
Expansion joints seem to be spaced sometimes miles apart which would explain why it starts when the train is a long way off. When the first wheel hits the start of the piece of track you are standing by this would obviously cause a vibration to shoot up and down the steel (as you mentioned). It would get quieter again as the train gets closer due to the trains weight being on it consistently rather than the initial 'strike' of the tuning fork. Cool. Unless anyone can add anything further, that will be my new assumption thanks guys

 

[Yabbadabba]

If it's in the third rail area your hearing this sound, could it be the sound of the shoe gear hitting the conductor rail ramps, how many pinging sounds do you hear before the train arrives?

 

[Equinox]

I guess it could be the shoe hitting the conductor, and the wheels striking the next section of track? Any length of metal will resonate when struck so could be a mixture of both?

 

[bronzeonion]

Most likely sound echoing along the rails, even on continuous welded rail you can hear the train passing over where the rails are joined as well as expansion joints of course and dont forgot points!

 

[Railsigns]

Continuous-welded rail has to have have expansion gaps every few hundred meters [metres], if it didn't then it would buckle in hot weather (well, more than it does already).

I don't believe it's correct to say that expansion gaps are provided at regular intervals on CWR. Expansion in CWR is accommodated by the rails being in tension. The expansion gaps ("adjustment switches") are installed only at certain locations, such as where CWR meets jointed track or switches and crossings.

 

[najaB]

Expansion in CWR is accommodated by the rails being in tension.

Not that I'm in any way doubting you, but do you know how this is achieved? It seems to me that the only way would be to heat the rails when they are installed.

 

[Railsigns]

Not that I'm in any way doubting you, but do you know how this is achieved? It seems to me that the only way would be to heat the rails when they are installed.

And heating is indeed how it is done, though if I recall correctly there's an alternative method whereby the rails are stretched by some kind of hydraulic apparatus.

 

[edwin_m]

Not that I'm in any way doubting you, but do you know how this is achieved? It seems to me that the only way would be to heat the rails when they are installed.

It used to be done that way but it is now done by stretching the rails with hydraulic rams by an amount calculated according to the length and the temperature at the time of laying, then cutting to length and welding up.

If done correctly this will set up a "stress free temperature" which is 27degC in the UK according to Wikipedia. Above this temperature the rail is in compression but if the ballast and sleepers are in good order they should be able to keep it in place up to the highest temperatures it is likely to encounter.

I've a feeling if rail is being laid in temperatures higher than the SFT that it needs to be re-stressed on a cooler day.

Some tracks have insulated joints in them for separating the "track circuits" that are used to detect trains, though these are not universal as some track circuits are jointless and some lines use axle counters instead. Possibly the "ping" is related to a train going over one of these insulated joints.

 

[swt_passenger]

Rails are stressed by hydraulic/mechanical pulling equipment to the condition where they would be stress free at 27 degrees C. (i.e. neither in tension or compression). Although this is referred to as the 'stress free temperature', it doesn't mean any heating is involved in the process.

It would be impossible to heat welded rail in the typical lengths it is installed in.

 

[najaB]

It would be impossible to heat welded rail in the typical lengths it is installed in.

That's what I was wondering about. Thanks.

 

[Bald Rick]

It would be impossible to heat welded rail in the typical lengths it is installed in.

The Harsco track renewal train bought by Jarvis for the West Coast modernisation did heat the rails as they were installed, using socking great propane burners. Apparently this is common in the US. It didn't last long.

 

[Marklund]

Hi guys

Just been having a discussion with someone about 'that' noise the rail track makes shortly before a speeding train passes.

The noise I am talking about is a high pitch 'pinging ' sound which seems to resonate/bounce quickly along a section of track before a train speeds past.
It doesn't seem like a vibration resonance from the train wheels, as it seems to start too suddenly.

Does this noise have an official 'name'?

I've always known this as the rails are "singing".

YouTube has a few videos.

 

[Equinox]

I've had a listen to a few... That seems to be a constant resonance which slowly gets louder... The noise I hear sounds very different. It it a lot sharper and starts instantly with a few stabbing noises like a lazer gun firing... It's hard to describe a sound! I'm sure people know what I mean though =/
I'm sure to does have something to do with the wheels hitting the start of that track section though. That would make sense.

Edit: Come to think of it they do seem to start singing after this point. So possibly the initial 'twang' of the wheels, followed by the constant resonance of the train on this piece of track would also make sense thanks by the way

 

[Marklund]

I do know what you mean. Lots of variables create different sounds, but I'm fairly sure it's the singing of the rails you're referring to. Different trains create different sounds, as does the railhead, and whether it's on a curve, or straight section.

If the Railhead Grinder has passed recently, the sound is completely different as to what it was before.

 

[david_VI]

I've had a listen to a few... That seems to be a constant resonance which slowly gets louder... The noise I hear sounds very different. It it a lot sharper and starts instantly with a few stabbing noises like a lazer gun firing... It's hard to describe a sound! I'm sure people know what I mean though =/
I'm sure to does have something to do with the wheels hitting the start of that track section though. That would make sense

I know the noise you mean. Always reminds me of the wires at the T rex paddock in Jurassic Park when they are cut.. ping like noise.

 

[Equinox]

I know the noise you mean. Always reminds me of the wires at the T rex paddock in Jurassic Park when they are cut.. ping like noise.

I found a video woo!

Can he heard here at 0:50. And also at 01:13, where you can see it actually happens when the train moves onto a new section of track.
http://m.youtube.com/watch?v=0mON7-xQKQI

Also here at 2:50
http://m.youtube.com/watch?v=i_DtBBdsC40


That double lazer-gun noise. I guess I always assumed it was electricity related as it sounds like the sort of noise electricity would make... Which come to think of it now sounds ridiculous lol

It would make sense that was the vibration caused by sets of wheels hitting parts of the track due to the timings of them/always seem to come in 2's.
I just like it... It's an awesome noise

And you're right... If you listen at 1:43... It's a very similar sound!
http://m.youtube.com/watch?v=1koa2xAxCAw

 

[Yabbadabba]

I'm quite convinced that is the sound of the shoe gear from the train as it hits the conductor rail ramp, the double ping you hear is because the class 444 has two lots of shoe gear on the leading coach.

If you stand at Three Bridges platform 5 and close your eyes, you can tell what stock is approaching by counting the pinging sounds as the trains hits the conductor rail ramp approaching the station, double ping followed pause by a double ping a single class 377, single ping pause single ping class 319 and ping pause ping pause ping pause ping class 442 just multiply if train consist of more than one unit. It can't be wheels passing over the rail joints as there are not enough pinging sounds to the amount of wheels on the train.

 

[najaB]

I'm quite convinced that is the sound of the shoe gear from the train as it hits the conductor rail ramp, the double ping you hear is because the class 444 has two lots of shoe gear on the leading coach.

That may be some of what you hear, but I've heard pretty much the same sound in non-electrified areas.

 

[Equinox]

There must be a railway engineer or two who use this forum to clarify either way?... Otherwise I might just send them an email and ask. It'll annoy me not knowing for sure!

 

[Warbonnet]

There must be a railway engineer or two who use this forum to clarify either way?... Otherwise I might just send them an email and ask. It'll annoy me not knowing for sure!

Im a team leader / track chargeman for Network rail, Ive been on the railway for just shy of 20 years.

Ive watched those video's in your examples and Yabbadabba is absolutely correct. The noise you hear is the shoe gear striking the con rail ramps. At speed if you watch them, you'll see them bounce causing a very quick double strike. Its rather like clobbering the rail with a hammer.

Also, as someone already pointed out, the con rail is live ALL the time, 24-7 unless overnight engineering work is happening on that particular circuit. It should always be treated as live and dangerous. The same goes for OHL electrification.
--- old post above --- --- new post below ---
In regard to installing CWR.
It is indeed pre stressed using hydraulic stressing equipment, sometimes called 'tensors'.
They physically pull the rails before the measured gap is Thermite welded. The amount it is pulled varies depending on curvature if any, rail temperature and the length to be pulled. Installing this pre stress in the rail gives it some where to go when the rail gets hot in the sun.
Expansion joints or as we call them 'adjustment switches' or 'breather switches' are only used at the end of CWR where it goes to jointed rails, or next to switches and crossings- aka point work. Some point work cannot be stressed as it is not strong enough - the stress would break and shear components like bolts etc. Some point work called 'reinforced S&C' can be stressed and so does not need an adjustment switch at each end adjacent to CWR. You'l see this type of S&C on concrete bearers usually.
Hope that makes some sense of it all.