Track noise

[Equinox]

Wow great explanation. Thanks very much for that! That's interesting to know as I've always wondered
I do notice that the faster a train approaches the closer together and more 'bouncy' the sound is.

I am a roller coaster engineer (or was) at Alton towers and love learning how things work.... Obviously a roller coaster train and a 'train train' are completely different in their workings so it's nice to have someone explain it clearly etc
Thanks again

 

[contrex]

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...

People have been fatally juiced because of believing the third rail is only live "when a train is coming".

 

[Equinox]

People have been fatally juiced because of believing the third rail is only live "when a train is coming".

As someone who also used to answer 999 calls I can honestly say I dealt with at least 3 fatalities over the 6 years I worked there, all related to children on the line who possibly had this misconception. One of which was burnt so badly they had actually turned black. (Apologies for the graphic description). Also had several calls of 'youths' placing large metal objects or logs onto the tracks to try and derail a train (which was always treated as a priority call). Quite how children go from boredom, to attempting mass murder is beyond me.

I personally thought maybe this may be the case due to my previous work on roller coasters, which rely on sets of proxy switches 'activating' the next block section. Eg, when the brake run detects the train is in the correct place and the train in front is clear of the station block, it then supply's power to the station motors pulling the previous train in.
Not that as an adult I would ever walk onto train tracks under any circumstances anyway. I think this is one of the first things they teach you at school as a child. Shame that some people don't seem to take it seriously

 

[SpacePhoenix]

http://www.youtube.com/watch?v=i_DtBBdsC40

About 2:42 as the train approaches FulWell. I've always noticed the sound more when it's a train approaching the station where it's going to stop at the station

 

[david_VI]

Great explanation but i'm also sure i've heard it on OLE area's. I've rarely left an OLE area and been near third rail.

 

[sutty]

It can't be purely third rail related, as I've heard it all over the network. I've also known it as the rails "singing" - the vibration of tonnes of train makes some interesting sounds.

There was a case recently (saw it on this forum) of a lad from India, I beleve who put his ear to the rail to listen for a train, but put his ea to the third rail.

 

[Cambo_flyer]

CWR does NOT have regular expansion gaps every few hundred metres. To prevent buckling it is stretched to the length it would be on a warm day before being welded up and fastened down. The whoosh you hear as a train approaches is because sound waves from the wheel sets travel much faster through steel than the air.

 

[AM9]

I remember as a child standing on the platform at tube stations hearing strange noises from the track when a train was approaching. There were 'twanging' noises sounding like the noise heard from trolleybus wires. There was also an underlying whirr which I assume was from the rolling action of the wheels. The sound was much clearer in the confinement of a tube station platform tunnel.
A similar noise can be heard on modern concrete sleepered track, particularly that laid for heavy fast traffic as on the GE main line. It didn't seem to be so noticeable from old wooden sleepered (particularly bullhead) track. Although the tube track then was all bullhead, in underground stations, there was a concrete trackbed and for the centre conductor rail, it was suspended above the 'suicide pit' on pillars. This would have the effect of acting like a guitar sound box.
It's much more noticeable on modern track formations as the track is on concrete sleepers with pandrol or similar clips and the whole assembly is tensioned and held much tighter in well maintained ballast. I imagine that rail steel alloys are also much harder causing the rail to propagate vibration and noise much further. This would seem to be a driver for rubber isolation on high speed tracks in sensitive locations.

p.s. I had trouble finding this thread having noticed it yesterday. Logically it should be moved to 'Infrastructure & Stations' or even 'UK Railway Discussion' as it doesn't have any connection with specific stock.

 

[fowler9]

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.

I would have thought that every single join in the running rail or conductor rail will be completely unique to an extent (Modern engineering minimizing differences) and that as such as a wheel or pick up shoe strikes it the tone and volume will be different.

 

[contrex]

I dealt with at least 3 fatalities ... related to children on the line who possibly had this misconception.(

I read a newspaper account of a fatality somewhere in Kent, near Margate perhaps, where a group of teenagers had been in the habit of using the railway as a shortcut to the beach. One of them, a girl of 14, tripped and fell on the juice rail and died. The others told the police they thought the rail was "only live when a train was coming".

 

[Class172]

Great explanation but i'm also sure i've heard it on OLE area's. I've rarely left an OLE area and been near third rail.

Agreed, I heard it this morning whilst waiting at the station - it cannot be caused by 3rd rail else we wouldn't hear it anywhere else...

 

[Bill Stanier]

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).

Thanks for that info - it's something I've often wondered about. But why is the 'stress free' temp set at 27C? That's a hot day in UK. Wouldn't something like 18C or 20C be a better 'stress free' temp? Is it because even on a hot day the rail engineers want the track still to be in tension rather than compression? Only on VERY hot days (above 27C) would it be in compression?

 

[edwin_m]

Thanks for that info - it's something I've often wondered about. But why is the 'stress free' temp set at 27C? That's a hot day in UK. Wouldn't something like 18C or 20C be a better 'stress free' temp? Is it because even on a hot day the rail engineers want the track still to be in tension rather than compression? Only on VERY hot days (above 27C) would it be in compression?

That's about it - like most metal things the rail is more able to withstand tension than the same amount of compression.

It's also true that, for example, an east-west rail in a cutting exposed to the sun but shielded from the wind can get a good deal hotter than the ambient temperature.

 

[Bald Rick]

Thanks for that info - it's something I've often wondered about. But why is the 'stress free' temp set at 27C? That's a hot day in UK. Wouldn't something like 18C or 20C be a better 'stress free' temp? Is it because even on a hot day the rail engineers want the track still to be in tension rather than compression? Only on VERY hot days (above 27C) would it be in compression?

The track maintenance standard explains it all.

But in short, in summer the effect of the sun lifts the temperature of the rail by between 8C (full cloud cover) and 18C (blue sky) above ambient shade temperature.

The rail temperature at which the expansion stress has the potential to start causing buckles on normal, plain track in good condition is 32C above stress free temperature. So, an SFT (stress free temperature) of 27C means that rail temperature has to reach 59C before mitigation measures are made (a 30/60mph blanket speed restriction on all lines in this case). And a rail temp of 59C in high summer, with blue sky, (worst case) requires a shade air temperature of 41C. And that is something that has never been recorded in this country.

An SFT of say 20C knocks 7C off all the above, ie a shade air temperature of 34C would require the same speed restriction. And we do have plenty of days in recent history with that temperature.

Hope this explains.

 

[Bald Rick]

Sorry, duplicate post (again).

 

[Hyphen]

Great explanation but i'm also sure i've heard it on OLE area's. I've rarely left an OLE area and been near third rail.

I agree that it can't be 3rd rail causing the noise. The same noise is very clear to hear on Plat 1 at Chesterfield (where there's no electrification of any type). It's most clear when a non-stop Voyager is approaching - you can hear the 'pings' before you can see the train round the curve. Trains slowing to stop at the station do still make the noise, but it's a fair bit quieter.

 

[fowler9]

I agree that it can't be 3rd rail causing the noise. The same noise is very clear to hear on Plat 1 at Chesterfield (where there's no electrification of any type). It's most clear when a non-stop Voyager is approaching - you can hear the 'pings' before you can see the train round the curve. Trains slowing to stop at the station do still make the noise, but it's a fair bit quieter.

Could it be the large weight of a train being applied to the rail via the tiny area of a metal tire? Even a minuscule imperfection would produce some sound that would resonate along the rail.

 

[Bill Stanier]

That's about it - like most metal things the rail is more able to withstand tension than the same amount of compression.

It's also true that, for example, an east-west rail in a cutting exposed to the sun but shielded from the wind can get a good deal hotter than the ambient temperature.

Most interesting - thanks. What prevents the in-tension track from tending to move sideways (inwards) on curves to relieve that tension?

Also, I have seen pictures of 'scarf joints' in CWR (a joint not straight across the rail, but cut at a long angle along the rail). What are these for, and don't they affect gauge when the track 'slides'?

 

[Peter Mugridge]

Also, I have seen pictures of 'scarf joints' in CWR (a joint not straight across the rail, but cut at a long angle along the rail). What are these for, and don't they affect gauge when the track 'slides'?

They are designed so that the expanding end of the rail slides outwards and will thus not foul the flanges.

 

[Bill Stanier]

They are designed so that the expanding end of the rail slides outwards and will thus not foul the flanges.

But...

a) Won't the gauge be affected as it slides (goes wider the more it slides outwards).

b) And with the previous explanations regarding how thermal expansion is dealt with on CWR, why would you need a sliding joint anyway?

 

[Warbonnet]

But...

a) Won't the gauge be affected as it slides (goes wider the more it slides outwards).

No because the rails are machined so that gauge is not effected. They are also monitored and inspected regularly to guard against them closing or opening to much. The overlap is measured as is the gaps according to the ambient and rail temp. If the track it buts onto is maintained the way it should be then this never happens anyway.
No such thing as a 'scarf' joint. We have breather switches or adjustment switches.

b) And with the previous explanations regarding how thermal expansion is dealt with on CWR, why would you need a sliding joint anyway?

As I explained in my earlier post, number 30 on page 2 infact, the ADJ switch is not there for the benefit of CWR. It used next to CWR and track that cannot be pre stressed like S&C and jointed track.
Funnily enough after being in the engineering grade for nearly 20 years I know abit about this stuff!
--- old post above --- --- new post below ---

I agree that it can't be 3rd rail causing the noise. The same noise is very clear to hear on Plat 1 at Chesterfield (where there's no electrification of any type). It's most clear when a non-stop Voyager is approaching - you can hear the 'pings' before you can see the train round the curve. Trains slowing to stop at the station do still make the noise, but it's a fair bit quieter.

You are getting the subject confused by the noise the wheels make on the rails! A joint like an Insulated Rail Joint in CWR (IRJ or IBJ) will ALSO make a similar noise to those in the O'P's video's!
Please believe me, the noise you hear in the video examples ARE shoe gear striking the con rail ramps, Ive heard and seen it a million times in my career!! Wheels striking joints can sound similar but that's not what we hear there.

 

[Bald Rick]

Most interesting - thanks. What prevents the in-tension track from tending to move sideways (inwards) on curves to relieve that tension?

The ballast 'shoulder' - the ballast that is put either side of the sleepers and normally a little but higher than top of sleeper.

The risk is actually the other way; if the ballast shoulder is not there, a speed restriction of 20mph is imposed at a rail temperature of SFT +13c, and this reduces progressively if the curve is of a radius of 1500m or less.

 

[Warbonnet]

Ive made a schematic to show how and why we use adjustment switches.
Ive colour coded the rails to show what parts of the rail is stressed / under tension.

GREEN is unstressed. This could be a piece of jointed track or in the case of the picture, there is some S&C out of shot to the right which cannot be stressed.

YELLOW This is the adjustment switch.

BLUE This is what we term the 'anchor'. Its actually a lot longer than what ive coloured in the picture but for sake of making it easier to see everything, its rather short in the example. This part does what it says, it forms an anchor for the stressed rail beyond.

RED This is our stressed track. This length could be miles long. It matters not as long as its got the right amount of stress in it.

Some one mentioned what happens on curves and how come it doesn't straighten out?
That's what ballast is for. As well as support and drainage it always maintains alignment and stops it moving around.

 

[Dynamonic]

At 5:55 in this video, you can clearly hear some pulsey noises coming from a Class 170 DMU on a non-electrified stretch of line in Tamworth.

As other people have mentioned, I've heard the noise on loads of non-electrified lines.

I love the noise!

 

[fowler9]

Ive made a schematic to show how and why we use adjustment switches.
Ive colour coded the rails to show what parts of the rail is stressed / under tension.

GREEN is unstressed. This could be a piece of jointed track or in the case of the picture, there is some S&C out of shot to the right which cannot be stressed.

YELLOW This is the adjustment switch.

BLUE This is what we term the 'anchor'. Its actually a lot longer than what ive coloured in the picture but for sake of making it easier to see everything, its rather short in the example. This part does what it says, it forms an anchor for the stressed rail beyond.

RED This is our stressed track. This length could be miles long. It matters not as long as its got the right amount of stress in it.

Some one mentioned what happens on curves and how come it doesn't straighten out?
That's what ballast is for. As well as support and drainage it always maintains alignment and stops it moving around.

Many thanks for all the info chief. It has certainly opened my eyes to a few things.

 

[Equinox]

At 5:55 in this video, you can clearly hear some pulsey noises coming from a Class 170 DMU on a non-electrified stretch of line in Tamworth.

As other people have mentioned, I've heard the noise on loads of non-electrified lines.

I love the noise!

Yeah I hear it it's just after the 5:55 you mentioned, but it's definitely there!
I can't see any obvious cause for this noise in this video though? No expansion gaps etc?

 

[Cambo_flyer]

I think its the train passing over a block joint.

 

[Warbonnet]

I think its the train passing over a block joint.

Absolutely correct. Its the wheels passing over a block joint aka IRJ- Insulated rail joint used for track circuit blocks.
Its a much different noise to shoe gear hitting the ramps in the earlier video's.

 

[Bill Stanier]

Ive made a schematic to show how and why we use adjustment switches.
Ive colour coded the rails to show what parts of the rail is stressed / under tension.

GREEN is unstressed. This could be a piece of jointed track or in the case of the picture, there is some S&C out of shot to the right which cannot be stressed.

YELLOW This is the adjustment switch.

BLUE This is what we term the 'anchor'. Its actually a lot longer than what ive coloured in the picture but for sake of making it easier to see everything, its rather short in the example. This part does what it says, it forms an anchor for the stressed rail beyond.

RED This is our stressed track. This length could be miles long. It matters not as long as its got the right amount of stress in it.

Some one mentioned what happens on curves and how come it doesn't straighten out?
That's what ballast is for. As well as support and drainage it always maintains alignment and stops it moving around.

Many thanks Warbonnet for clear and concise explanation. Much appreciated!

 

[Warbonnet]

Your welcome chaps!