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Changing cant?

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sprunt

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There is a notice on the edge of platform 1 at Limehouse station, visible from platform 2, saying (words to the effect of - I can't remember the exact wording) "CHANGING CANT ON THIS BRIDGE IS NOT PERMITTED".

What is changing cant? I have attempted to search for the term, but the results are just overwhelmed by Google interpreting "cant" as "can't".
 
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HOOVER29

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Height or angle of the track.
No doubt someone will be along in a mo with a more technical answer
 

furnessvale

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Cant is the super-elevation of one rail above the other enabling curving.

When cant is changed, not only is the speed ability on a given curve altered, but the position of the loading gauge, relative to the structure is also changed.

In tight locations such a change could bring loading gauge and structure gauge into conflict.
 

jmh59

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aka superelevation, its where one rail is raised relative to the other e.g. on curves the train is trying to slide off sideways so raising that rail caters for the cornering forces (someone else will hopefully come up with a far better explanation but basically that's it) - think of a banked race track. The danger of altering it in the case you mention is trains may then hit the bridge (or indeed other stuff)
 

sprunt

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Thanks, that all makes sense. So this sign is aimed at track workers rather than anyone involved in operating the train then?
 

axlecounter

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Is this common practice or some artist’s work to assure that cant doesn’t get changed? Surely there must be paper somewhere that specifies this?
 

quantinghome

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It may be a weak bridge. Changing cant changes the volume of ballast which can have a significant effect on the load applied to the bridge structure.
 

Wychwood93

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An impact on the 'kinetic envelope' would also be there - an odd but relevant issue. Platform clearances etc. rely on the 'kinematic envelope' see:
http://www.railsystem.net/structure-gauge-and-kinematic-envelope/

Or: https://en.wikipedia.org/wiki/Loading_gauge

If new stock is proposed, then said stock is run through the new route to see whether itself or the platforms, let alone other structures are too close or... worst case, in contact. Others on this forum may have more than my basic understanding.
 

Boodiggy

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An impact on the 'kinetic envelope' would also be there - an odd but relevant issue. Platform clearances etc. rely on the 'kinematic envelope' see:
http://www.railsystem.net/structure-gauge-and-kinematic-envelope/

Or: https://en.wikipedia.org/wiki/Loading_gauge

If new stock is proposed, then said stock is run through the new route to see whether itself or the platforms, let alone other structures are too close or... worst case, in contact. Others on this forum may have more than my basic understanding.


A lot of work is done prior to new rolling stock running but no traffic can run if not cleared for a route to check it fits. That would be far to dangerous. There are various systems used such as clear route that model clearances. Gauging management is far more complex than most people realise.
 

Pshambro

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There is a large amount of cant on what I think is line 1 out of Paddington (just before North Pole), being a low speed section without a noticeable sharp bend I have always wondered why it is there. No structures near the line and adjacent lines don’t seem to have nearly as much.
 

edwin_m

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There is a large amount of cant on what I think is line 1 out of Paddington (just before North Pole), being a low speed section without a noticeable sharp bend I have always wondered why it is there. No structures near the line and adjacent lines don’t seem to have nearly as much.
Cant can increase the speed even on low-speed sections.
 
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We dont have "super elevation" in the UK, its called track cant and is given in degrees from the horizontal plane on which the track sits.

A track cant of say 11° would give three things. First it would raise the level of the track, thus the height of the train (so a train that could fit under a bridge at 0° of cant couldnt fit at 11° of cant) secondly it would make a trains wider as it would lean over to one side while on that canted section, thus a train that was wide enough is now to wide... Third is would allow a train to travel faster over that curve.

A track cant gives a banked section of track.
We're not American and dont use American terminology here in the UK.
 

furnessvale

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We dont have "super elevation" in the UK, its called track cant and is given in degrees from the horizontal plane on which the track sits.

A track cant of say 11° would give three things. First it would raise the level of the track, thus the height of the train (so a train that could fit under a bridge at 0° of cant couldnt fit at 11° of cant) secondly it would make a trains wider as it would lean over to one side while on that canted section, thus a train that was wide enough is now to wide... Third is would allow a train to travel faster over that curve.

A track cant gives a banked section of track.
We're not American and dont use American terminology here in the UK.
My copy of British Railway Track makes equal reference to both terms, as indeed we did when I worked in a perway drawing office some years ago.
 

edwin_m

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We dont have "super elevation" in the UK, its called track cant and is given in degrees from the horizontal plane on which the track sits.

A track cant of say 11° would give three things. First it would raise the level of the track, thus the height of the train (so a train that could fit under a bridge at 0° of cant couldnt fit at 11° of cant) secondly it would make a trains wider as it would lean over to one side while on that canted section, thus a train that was wide enough is now to wide... Third is would allow a train to travel faster over that curve.

A track cant gives a banked section of track.
We're not American and dont use American terminology here in the UK.
Having worked on both British and international projects I'd agree "cant" is the generally used term in the UK but "superelevation" is more widely understood internationally and UK rail engineers will understand it.

Incidentally 11° is a very large amount of cant. It is normally measured in distance of one rail above the other and by coincidence on standard gauge one degree is about one inch. The normal maximum is about six inches.
 

Ploughman

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In more than 30 years on the track I have never used Degrees.
Always used Millimeters with a max of 150 mm unless on exceptional circumstances.

Superelevation as a term is used when liasing with Highways staff who use it on roads, or when explaining to non railway people.
 

kieron

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Superelevation as a term is used when liasing with Highways staff who use it on roads, or when explaining to non railway people.
Meanwhile, the road signs they erect call it "camber" instead.

What intrigues me is why there's a sign saying not to change the cant on that bridge, and not just a note in the paperwork for it. Could someone just wander along during a posession, decide that the cant was wrong, and start doing something about it there and then?
 
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Having worked on both British and international projects I'd agree "cant" is the generally used term in the UK but "superelevation" is more widely understood internationally and UK rail engineers will understand it.

Incidentally 11° is a very large amount of cant. It is normally measured in distance of one rail above the other and by coincidence on standard gauge one degree is about one inch. The normal maximum is about six inches.

OMG...
It was just an example number because it was easier to write 11°. My finger was over the 1 key.

In more than 30 years on the track I have never used Degrees.
Always used Millimeters with a max of 150 mm unless on exceptional circumstances.

Superelevation as a term is used when liasing with Highways staff who use it on roads, or when explaining to non railway people.

That is exactly my thoughts too.
It depended on who you were talking to as to what you called it.
To somebody else on the railway it was the cant of the track or road.
Meanwhile, the road signs they erect call it "camber" instead.

What intrigues me is why there's a sign saying not to change the cant on that bridge, and not just a note in the paperwork for it. Could someone just wander along during a posession, decide that the cant was wrong, and start doing something about it there and then?

I would say its more likely due to some engineering works past of in the future. you would make things of importance out...
For example, and this is not to mean it is specific in this exact situation and not to say its done every time either. Its just a possible explanation of it.
You are told in your notes that the level of the track there is most important and that during the rail relay the track level and cant can not be changed from what it is, so you would mark it so the crews know the track there must go back to the original levels.
 

Joseph_Locke

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Mathematically, an angle is the sound way to do it, as measuring the elevation of one rail over the other ignores the issue that the adjacent side of the triangle gets shorter. However, marking degrees up on sleepers (at any reasonably small increment) would require fractions and the error is actually particularly significant (due to the large margin of safety inherent in the way the railway does these things). Worth noting that the industry does use cant (the designed value) and crosslevel (the measured value).
 

LNW-GW Joint

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We're not American and dont use American terminology here in the UK.

We increasingly do - "S&C" for instance (switches and crossings).
Not to mention all the US-led tech terms in the IT and media worlds, which increasingly impact on the UK railway.
Even Network Rail uses the term "train station".
Greater use of international standards will also normalise such terms.
We "don't use kilometres" but that won't stop railway routes being measured in km for ERTMS signalling, with km speedos in the cab.
 

furnessvale

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In more than 30 years on the track I have never used Degrees.
Always used Millimeters with a max of 150 mm unless on exceptional circumstances.

Superelevation as a term is used when liasing with Highways staff who use it on roads, or when explaining to non railway people.
In the early 1960s, we had several curves between Penrith and Carlisle where, by special allowance, the cant was 7 inches. I believe these curves are all now back to 6 inches.
 

superkev

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I seem to remember some other countries permit either higher cants or higher speeds on curves than in the uk. Anyone confirm.
K
 

furnessvale

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I seem to remember some other countries permit either higher cants or higher speeds on curves than in the uk. Anyone confirm.
K
Certainly higher speeds for any given cant as cant deficiency in many other countries is greater.

Quite noticeable in some countries as you are pushed towards the side of the coach when cornering.
 
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We increasingly do - "S&C" for instance (switches and crossings).
Not to mention all the US-led tech terms in the IT and media worlds, which increasingly impact on the UK railway.
Even Network Rail uses the term "train station".
Greater use of international standards will also normalise such terms.
We "don't use kilometres" but that won't stop railway routes being measured in km for ERTMS signalling, with km speedos in the cab.

Are you sure S&C is an American term?
If it is its a very old one. Ive know it used since the 60s.
A set of points that put you to the left for instance is a left hand facing switch, but commonly used terms are points...
And crossings are crossings...
 

quantinghome

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Are you sure S&C is an American term?
If it is its a very old one. Ive know it used since the 60s.
A set of points that put you to the left for instance is a left hand facing switch, but commonly used terms are points...
And crossings are crossings...
I suspect it's the difference between vernacular and technical English which we have always used, and it just happens that American English adopted our technical terms rather than the everyday ones. It's the same with road engineering, where 'highway' and 'pavement' are used in a technical context.
 

Wychwood93

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Certainly higher speeds for any given cant as cant deficiency in many other countries is greater.

Quite noticeable in some countries as you are pushed towards the side of the coach when cornering.
Cant deficiency in France is greater - and more fun! - seriously, the downside is wear on wheels and rails - they have, obviously, done the sums. Correct me if I am wrong, but unlikely to be the case on LGV (high speed) lines.
 

DelW

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Meanwhile, the road signs they erect call it "camber" instead.
From my memory of setting out new roads, admittedly over 30 years ago, it was a camber when the centreline was higher than the kerb lines, and superelevation when a kerb line was higher than the centreline (as on the outside of a bend).
 

Bald Rick

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Cant deficiency in France is greater - and more fun! - seriously, the downside is wear on wheels and rails - they have, obviously, done the sums. Correct me if I am wrong, but unlikely to be the case on LGV (high speed) lines.

SNCF use a maximum cant deficiency of 150mm, which is the same as the exceptional value used on NR (on the Berks & Hants, ECML North, and MML, amongst other locations).

However on the LGVs, a maximum can’t deficiency of 100mm is used, which is the same as the maximum ‘normal’ value on NR.
 
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