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Post by quex on Nov 18, 2020 10:58:22 GMT
This might sound a bit of a stupid question, but what gauge is the Underground?
I vaguely remember reading somewhere (I think it may have been one of the later editions of H F Howson's London's Underground) that the track is maintained to a nominal gauge that ISN'T the standard 1435 mm, it was something like 5-10 mm wider to allow for greater lateral play. Am I right in thinking this, and does anyone have the exact nominal value?
I should make clear that this is distinct from gauge widening of sharp curves, where the gauge may be increased by anything up to an inch.
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Post by 100andthirty on Nov 18, 2020 14:58:46 GMT
I'm sure a track expert will come along but I believe there is some dispute about whether the nominal gauge is 1435 mm or 1432 mm. However there is no truth in the suggestion what any wider value is used. On ordinary plain line a tolerance of +/- 3 mm is allowed.
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Post by revupminster on Nov 18, 2020 17:23:40 GMT
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Post by quex on Nov 18, 2020 19:20:30 GMT
I'm sure a track expert will come along but I believe there is some dispute about whether the nominal gauge is 1435 mm or 1432 mm. However there is no truth in the suggestion what any wider value is used. On ordinary plain line a tolerance of +/- 3 mm is allowed. This could well be what I was thinking of - as I say it's something I only very vaguely recall and perhaps I remembered in the "wrong direction". Thanks! Come to think of it, I think I might have got the "lateral play" idea confused with the extra quarter-inch added to Brunel's broad gauge... My 1999 book The Railway Data File says that standard gauge is now 4ft 8 and 1/8 because a tighter fit of wheel to rail gives greater stability. Interesting you should say that, I think I've got a copy of that book buried away somewhere. I've got a good excuse to dust it off now! |
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Post by 100andthirty on Nov 19, 2020 7:51:13 GMT
I'm sure a track expert will come along but I believe there is some dispute about whether the nominal gauge is 1435 mm or 1432 mm. However there is no truth in the suggestion what any wider value is used. On ordinary plain line a tolerance of +/- 3 mm is allowed. This could well be what I was thinking of - as I say it's something I only very vaguely recall and perhaps I remembered in the "wrong direction". Thanks! Come to think of it, I think I might have got the "lateral play" idea confused with the extra quarter-inch added to Brunel's broad gauge... My 1999 book The Railway Data File says that standard gauge is now 4ft 8 and 1/8 because a tighter fit of wheel to rail gives greater stability. Interesting you should say that, I think I've got a copy of that book buried away somewhere. I've got a good excuse to dust it off now! "The tighter fit of wheel to rail leads to.............." more wear not better stability. 4 ft 8in and 1/8 is 1425 mm and by any standard that's a tight gauge. As an illustration, up to the 1990s the Victoria line was bedevilled by tight gauge (a construction legacy) causing significant wheel wear before a special thin flange wheel profile was adopted. |
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Post by 100andthirty on Nov 19, 2020 7:54:07 GMT
As a postscript, there is one type of track on the underground where 'tight gauge is allowed and that's on depot roads where height setting is carried out to ensure the wheels are properly centred between the rails.
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Post by barrybahamas on Nov 21, 2020 1:09:52 GMT
I thought I heard somewhere that in the 1800's, because of the spread of railways in the UK and with many railway companies opting for different gauges, an act of Parliament was passed stating that all future railways would have to be 4' 8 1/2" - to encourage connectivity and create a "national rail". If so, surely LU would have to comply with that.
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Post by brigham on Nov 21, 2020 8:28:16 GMT
I thought I heard somewhere that in the 1800's, because of the spread of railways in the UK and with many railway companies opting for different gauges, an act of Parliament was passed stating that all future railways would have to be 4' 8 1/2" - to encourage connectivity and create a "national rail". If so, surely LU would have to comply with that. 'An Act for regulating the Gauge of Railways' 1846. This act set the Standard Gauges for Great Britain (except SW England & Wales) and Ireland. The London Underground complies with it; the Glasgow subway does not. Parliament can authorise the building of a railway to any other gauge it chooses, of course. It MAY have made sense for the Channel tunnel railway, and such new railways associated with, to have been built to a mixed gauge, incorporating a broader gauge as well as the standard one. |
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Post by revupminster on Nov 21, 2020 13:39:44 GMT
The first underground line Paddington-Farringdon (1863) and it's extension (1864) to Hammersmith were dual gauge (standard and wide) and operated GWR locos and stock for the first few years.
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Post by Chris M on Nov 21, 2020 13:51:13 GMT
Parliament can authorise the building of a railway to any other gauge it chooses, of course. It MAY have made sense for the Channel tunnel railway, and such new railways associated with, to have been built to a mixed gauge, incorporating a broader gauge as well as the standard one. The relevant act deals with track gauge, which is the same at both ends of the Channel Tunnel, not loading gauge. |
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Post by norbitonflyer on Nov 21, 2020 15:09:50 GMT
The relevant act deals with track gauge, which is the same at both ends of the Channel Tunnel, not loading gauge. It will be an issue if we ever get a crossing of the Irish Sea though. But the Spanish cracked that problem over 50 years ago |
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Post by brigham on Nov 21, 2020 15:23:55 GMT
Parliament can authorise the building of a railway to any other gauge it chooses, of course. It MAY have made sense for the Channel tunnel railway, and such new railways associated with, to have been built to a mixed gauge, incorporating a broader gauge as well as the standard one. The relevant act deals with track gauge, which is the same at both ends of the Channel Tunnel, not loading gauge. I'm referring to track gauge. |
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Post by rincew1nd on Nov 21, 2020 16:20:54 GMT
Can we stick to LU track gauge please?
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Post by Tom on Nov 21, 2020 17:44:22 GMT
As a postscript, there is one type of track on the underground where 'tight gauge is allowed and that's on depot roads where height setting is carried out to ensure the wheels are properly centred between the rails. Likewise around Piccadilly Circus crossover on the Bakerloo line, the track gauge widens to (from memory) 1450mm. |
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Post by 100andthirty on Nov 22, 2020 8:29:03 GMT
Tom has highlighted one curve, but gauge widening is allowed and necessary on small radius curves.....the smaller the radius, the more widening. Apart from the circumstance I mentioned above, gauge tightening is never a good thing.
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Post by rincew1nd on Nov 22, 2020 17:52:29 GMT
I'm sure a track expert will come along but I believe there is some dispute about whether the nominal gauge is 1435 mm or 1432 mm. However there is no truth in the suggestion what any wider value is used. On ordinary plain line a tolerance of +/- 3 mm is allowed. I know that I asked the discussion to stick to LU track gauge, but I've just come across this tweet from a railway lecturer which may shed some light on the above point: |
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Post by 100andthirty on Nov 22, 2020 18:29:12 GMT
As someone old enough to remember the transition from imperial to metric measurement, I have observed that people were much more precise with metric dimensions than with imperial.......probably me too! In the old days is someone stated that a dimension was, say, 4' 8 3/8" they might say that 'it's only 1/8" smaller than the right dimension". However in metric if someone says the dimension is 1432 mm, then the remark might be 'oh, that's 3 mm smaller than the right dimension', with an implication that 3 mm is a lot, despite the fact that its just 1/8"!
Another of the challenges with track is measuring the gauge with a train on the track will give a different result than if the track is measured unloaded. Coned wheels on inclined rails leads to a tendency to spread the gauge against the tension of the rail clips.
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Post by rincew1nd on Nov 22, 2020 19:53:59 GMT
I agree, imperial is a great system for rough measurements. However as things have become more precise and/or computerised then the base ten metric system is becomes so much easier to work with than the imperial system which changes base depending on what you are measuring.
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Post by quex on Nov 22, 2020 23:29:36 GMT
I thought I heard somewhere that in the 1800's, because of the spread of railways in the UK and with many railway companies opting for different gauges, an act of Parliament was passed stating that all future railways would have to be 4' 8 1/2" - to encourage connectivity and create a "national rail". If so, surely LU would have to comply with that. I think the idea of a gauge of +/- a few mm over 1435 mm is that it would still permit most standard gauge rolling stock without too much difficulty - i.e. it's not different enough to be "properly" different, but is different enough to have influence over factors like rail/wheel wear and bogie movement. It's exactly why I posed my OP question but it's surprising there's so much discussion over track gauge - you'd think there'd be a simpler answer but it's not a clear-cut issue! I've just come across this tweet from a railway lecturer which may shed some light on the above point... Again, that sounds like the sort of thing I was originally thinking of, but I didn't realise it had been policy on the big railway. I'd be surprised if hunting was as large an issue on LU though, due to the lower speeds generally - unless LU treads have a greater conicity than your typical mainline stock? |
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Post by marri260 on Nov 22, 2020 23:43:00 GMT
It's been a long time since I was on the PW lectures, but from memory bullhead track is 1435mm and flat bottom is 1432mm, with up to 3mm gauge widening on curves.
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Post by Chris M on Nov 23, 2020 1:29:04 GMT
I'd be surprised if hunting was as large an issue on LU though, due to the lower speeds generally - unless LU treads have a greater conicity than your typical mainline stock? I don't know about LU, but the DLR does suffer from quite bad hunting on the higher speed sections and I believe this is due to the wheel profiles used to negotiate the very tight corners on the system. I couldn't say whether that's increased conicty or some other aspect of the profile though. |
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Post by Tom on Nov 23, 2020 6:15:27 GMT
It's been a long time since I was on the PW lectures, but from memory bullhead track is 1435mm and flat bottom is 1432mm, with up to 3mm gauge widening on curves. I thought it was one dimension for plain line (1432mm I think) and 1435 for points and crossings, but I could well be wrong. |
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Post by North End on Nov 23, 2020 14:31:29 GMT
I'd be surprised if hunting was as large an issue on LU though, due to the lower speeds generally - unless LU treads have a greater conicity than your typical mainline stock? I don't know about LU, but the DLR does suffer from quite bad hunting on the higher speed sections and I believe this is due to the wheel profiles used to negotiate the very tight corners on the system. I couldn't say whether that's increased conicty or some other aspect of the profile though. This is exactly it - there’s a trade-off between wear and riding qualities on sharp curves versus hunting on straight sections. LU seems to go for the former, which is quite plain to see when one sees the way LU trains generally negotiate curves roughly. Used to be very bad on DLR, though seems to have improved, though I don’t use DLR much these days so others may know better on that! |
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Post by d7666 on Dec 30, 2020 2:16:56 GMT
As someone old enough to remember the transition from imperial to metric measurement, I have observed that people were much more precise with metric dimensions than with imperial.......probably me too! In the old days is someone stated that a dimension was, say, 4' 8 3/8" they might say that 'it's only 1/8" smaller than the right dimension". However in metric if someone says the dimension is 1432 mm, then the remark might be 'oh, that's 3 mm smaller than the right dimension', with an implication that 3 mm is a lot, despite the fact that its just 1/8"! Spot on. I usually word it slightly differently - 4 ft 8.1/2 in suggests "to the nearest 1/2 inch"; but that track gauge is not exactly 56.500000 in, but 56.5 in +/- a tolerance, a tolerance for most purposes less than 1/2 in, so no-one mentions it. What happens is people insist on doing the precise conversion to 1435 mm in turn that is suggesting "to the nearest mm" then get hot under the collar when some one says e.g. 1430 or 1440 mm. That +/- 5 mm is still within the "1/2 in tolerance" if converted back. When BR went to 1432 mm, this was within the normal tolerance range of nominal 1435 mm, so that's how they could do it. And reverse that back to 1435 mm. Noting the mod comment to keep to LU, can I just add one digression that the GB 1435 to 1432 mm was not the only example; the Soviets went from 1524 mm to 1520 mm for their nominal "5 ft" guage"; and elsewhere in the world some 3 ft 6 in ('colonial' or 'cape' gauge) users (South Africa for one) went from the usual 1067 to 1065 mm. No idea if those place's revised values are still in force or if they have reverted. |
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Post by trog on Apr 26, 2021 10:45:15 GMT
I don't know if LU has followed suit but on the mainline railway track gauge has changed several times over the last few decades. From 4'-8 1/2" to 1432mm in the 1970's, then to 1435mm in the early 1980's, then in 1999 new track with CEN60 rail started to be laid at 1438mm gauge.
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Post by roythebus on Apr 26, 2021 22:14:31 GMT
Sound like I.K.Brunel was right after all and we're slowly adopting his gauge by stealth.  |
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Post by burkitt on Apr 26, 2021 22:53:09 GMT
Very sneaky! At three millimeters per decade, we'll all be running on GWR broad gauge no later than the mid 42nd century!
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Post by brigham on Apr 27, 2021 7:37:28 GMT
Sound like I.K.Brunel was right after all and we're slowly adopting his gauge by stealth. A bit like the Metric System... |
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