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Post by norbitonflyer on Dec 31, 2020 12:27:38 GMT
I often mused, as regular user of the Drain, on what would be the effect on capacity and average end-to-end journey time (as waiting time would be zero) if the Travolator went all the way to Waterloo
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Post by peterc on Dec 31, 2020 15:36:05 GMT
also wonder if its trains would be Standard gauge - for a self-contained system there would be no logical need for this, wider trains could possible make greater sense than ultra long trains. A wider gauge railway would have no scope for interoperability, increased costs of rolling stock due to being non-standard, issues with delivery and disposal of stock, etc. It would also necessitate tunnels with a larger diameter still, and tunnelling costs increase significantly with diameter (iirc the amount of spoil to be dealt with increases with the cube of the diameter). A larger loading gauge on standard gauge track has fewer of these issues, but it still not a panacea. The BART system in San Francisco uses a broad gauge (5'6") but this has not been regarded as a success and any new lines are likely to be standard gauge. If we were starting from scratch would interoperability be an issue? We no longer run excursions from Ealing to Southend or need to deliver coal at surface stations after all. I can see the value of staying with standard guage as it reduces the need for bespoke equipment but is it really the optimum? |
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Post by 100andthirty on Dec 31, 2020 16:08:10 GMT
For any city considering a Metro, they start with a few basics.
1) How many passengers per hour per direction
2) It will be powered by electricity
3) The tunnel will be big enough to accommodate trains that are roughly rectangular in cross section
4) There will probably be a side walkway
5) The trains will be tall enough to accommodate all the equipment and bogies under the floor without the wheels penetrating the floor to give maximum flexibility on interior and door layout.
6) The platforms will be level with the train floor and will be straight.
If this sounds like a deviation from the topic, all the above means that there will be space above the train for a conductor rail similar to that used on Crossrail and avoidance of ground based conductor rails, even very well insulated, is to be preferred. The above requirements, however, mean that there is no increased tunnel size to accommodate the overhead supply
Whether the power supply is AC or DC is somewhat moot. DC at 1500 V allows reasonable space between substations and is a metro standard. AC Traction are unpopular with the electricity distributors as they don't make balanced use of the three phases and the load can swing from 2-3 MW being taken from the supply to a similar amount of power being fed back into the supply all over a few seconds. Increasingly, two way power converters are being employed to avoid this problem. These take in three phase electricity and output single phase - and vice versa when trains are braking.
There is also a debate to be had as to whether regenerated energy is captured on train or all exported off train. On train energy capture would significantly reduce the load swings and reduce the power supply peak ratings. The external supply would provide power to the auxiliaries and for steady speed running with the battery (or other energy store device) providing top up for acceleration. Similarly, on braking, the regenerative brake would feed the auxiliaries and charge the battery with any surplus power going back to the line. Clearly there would be load swings, but not as severe.
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Post by Chris M on Dec 31, 2020 17:43:20 GMT
For any city considering a Metro, they start with a few basics. 1) How many passengers per hour per direction 2) It will be powered by electricity 3) The tunnel will be big enough to accommodate trains that are roughly rectangular in cross section 4) There will probably be a side walkway 5) The trains will be tall enough to accommodate all the equipment and bogies under the floor without the wheels penetrating the floor to give maximum flexibility on interior and door layout. 6) The platforms will be level with the train floor and will be straight. In other words, look at the DLR. Although the ridership was significantly underestimated for that system it gives a good idea of what a new metro system in the UK would look like - not perfect obviously as technology has moved on since the 1980s but not bad. |
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Post by zbang on Dec 31, 2020 18:29:07 GMT
I can see the value of staying with standard guage as it reduces the need for bespoke equipment but is it really the optimum?
Optimum in what sense? Certainly, it's optimum cost-wise (even bespoke equipment uses some standard parts). There may be a consideration of track geometry, and how curves & points, but I can't see that from here.
(doing this largely as an excersize because it interested me)
About the only other factor would be expected center-of-mass (CM) of the load. Since humans average under 6' tall and under 11-12 stone, it becomes difficult for the CM to get over maybe 2-2.5m above the rail. For the sake of discussion, if we assume a non-driving motor car weighs 20t and holds 270 people (~20t), the CM would only be maybe 1.8m above the rail (that's a guess) and centered. If only one side of the car had heavy riders (15 stone? each), that might be 60-70 people and 6-7t, but with respect to the overall weight the CM is still between the rails and relatively low (and that can be managed by super-elevating rails on higher-speed curves).
Feel free to check my assumptions, I'm not through my first cup of coffee. (Yes, I was intentionally mixing units  ). |
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Post by brigham on Jan 2, 2021 9:56:18 GMT
Stephenson's gauge is too narrow.
Brunel knew that, Hitler knew that, and Stephenson himself knew it.
It prevails because of legacy, not merit. It arose from the need to use existing wagons, and not from any engineering-based calculation.
The remarkable performance we have today is despite, not because of, the narrowness of the gauge.
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Post by 35b on Jan 2, 2021 16:10:38 GMT
Stephenson's gauge is too narrow. Brunel knew that, Hitler knew that, and Stephenson himself knew it. It prevails because of legacy, not merit. It arose from the need to use existing wagons, and not from any engineering-based calculation. The remarkable performance we have today is despite, not because of, the narrowness of the gauge. What obstacles has the narrowness of the track gauge caused? Both Brunel and Hitler were very keen on larger vehicles, but I'm not clear what advantages widening the track gauge would have had in terms of railway performance. |
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Post by zbang on Jan 2, 2021 18:36:20 GMT
Stephenson's gauge is too narrow. Brunel knew that, Hitler knew that, and Stephenson himself knew it. It prevails because of legacy, not merit. It arose from the need to use existing wagons, and not from any engineering-based calculation. I'm not sure I buy that. IIRC the Gauge Act (1846?) recommended standard gauge, so there was probably a decent understanding of the effects of narrow/wide even then, or at least of compatibility between companies; and since new rolling stock were being built for new companies, they could be built for whatever the company wanted. Even if Stephenson though it wasn't optimum*, that's what he built. Sure, companies did continue to build other gauges, but I suspect that was not from rational engineering considerations.
* I haven't turned up anything along those lines, would love to hear of any.
There has never been a lack of observers who thought 4 feet 8-1/2 was suboptimal - men as disparate as James J. Hill, David P. Morgan, and Adolf Hitler, to name three. Essentially, this interpretation is based on the fact that area-volume ratios of cylinders become more favorable as size increases. As a consequence, large boilers produce their output at a lower average cost than small ones
Certainly, by the time the tubes were being dug, standard gauge was well established and there wouldn't be much reason to consider otherwise.
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Post by brigham on Jan 4, 2021 8:45:10 GMT
Stephenson's gauge is too narrow. Brunel knew that, Hitler knew that, and Stephenson himself knew it. It prevails because of legacy, not merit. It arose from the need to use existing wagons, and not from any engineering-based calculation. The remarkable performance we have today is despite, not because of, the narrowness of the gauge. What obstacles has the narrowness of the track gauge caused? Both Brunel and Hitler were very keen on larger vehicles, but I'm not clear what advantages widening the track gauge would have had in terms of railway performance. No scientific knowledge is required. You only need look at the development of road motors to observe that larger motor lorries have a broader track than smaller ones. This is not a co-incidence. Stephenson's gauge is not unlike the Motion Picture Academy's frame rate. Set in stone by circumstances which no longer prevail. |
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Post by 35b on Jan 4, 2021 12:15:27 GMT
What obstacles has the narrowness of the track gauge caused? Both Brunel and Hitler were very keen on larger vehicles, but I'm not clear what advantages widening the track gauge would have had in terms of railway performance. No scientific knowledge is required. You only need look at the development of road motors to observe that larger motor lorries have a broader track than smaller ones. This is not a co-incidence. Stephenson's gauge is not unlike the Motion Picture Academy's frame rate. Set in stone by circumstances which no longer prevail. That may well be, but doesn’t answer my question about whether and why a broader standard gauge would have improved performance. |
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Post by brigham on Jan 4, 2021 13:10:01 GMT
No scientific knowledge is required. You only need look at the development of road motors to observe that larger motor lorries have a broader track than smaller ones. This is not a co-incidence. Stephenson's gauge is not unlike the Motion Picture Academy's frame rate. Set in stone by circumstances which no longer prevail. That may well be, but doesn’t answer my question about whether and why a broader standard gauge would have improved performance. No, it doesn't. It just gives you an example of how it does. The rest you can work out for yourself; same as I did. |
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Post by zbang on Jan 4, 2021 17:17:59 GMT
Show your workings?
A broad gauge might give some advantages, but to any competent engineer those must be quantifiable and then weighed against external factors such as space and cost. In a similar vein, comparisons of railway stock and permanent way to roadway lorries is tenuous as both the ways and vehicle suspensions have different characteristics (with the railway's being more tightly controlled and maintained).
So, what are the advantages of a broad gauge? (I'm guessing here, feel free to add)
Wider base for the same center of mass, makes it harder to tip. More space between the wheels for motors and other equipment.
Disadvantages? Possibly wider permanent way needed. Bespoke* bogies/wheelsets/etc, which leads to higher bespoke content of all track equipment, which leads to higher costs for little discernible improvement.
*at the national or even continental level
It's been said that SF's BART pays a 20% premium for the use of a broad gauge (can't find a reference to that at the moment). Also, possibly the most recently-built broad gauge system is BART, and when you look into it, the real reason appears to be so that only BART trains could run on those tracks.
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Post by brigham on Jan 4, 2021 18:27:15 GMT
Advantages:
Increased loading-gauge availability. The maximum feasible loading gauge is directly proportional to the rail gauge.
Disadvantages:
Wider permanent way IS needed. This would have increased INITIAL costs.
However, this needs to be amortised (BBC word there!) over the following years. A hundred and fifty years of impeded progress is a lot to pay for an initial saving of costs. Bear in mind that Stephenson's FIRST public railway would have cost very little more to build in a broader gauge, had the notion of using existing wagons not been to the fore.
The argument about 'bespoke' wheelsets is irrelevant. Had the Gauge Commission adopted Brunel's gauge as the standard, then bespoke wheelsets would not have been required.
In all, the Gauge Commission's decision was down to first cost. The same had already been applied to canals, leading to the bizarre 'narrowboat', and ultimately ensuring their demise as commercial carriers; and to the early two-lane motorways, which are currently costing more than their original construction did in widening schemes.
There must be many more schemes where the future has been mortgaged for short-term benefit. I personally believe that it is becoming more, rather than less prevalent.
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Post by 35b on Jan 5, 2021 8:31:47 GMT
Advantages: Increased loading-gauge availability. The maximum feasible loading gauge is directly proportional to the rail gauge. Disadvantages: Wider permanent way IS needed. This would have increased INITIAL costs. However, this needs to be amortised (BBC word there!) over the following years. A hundred and fifty years of impeded progress is a lot to pay for an initial saving of costs. Bear in mind that Stephenson's FIRST public railway would have cost very little more to build in a broader gauge, had the notion of using existing wagons not been to the fore. The argument about 'bespoke' wheelsets is irrelevant. Had the Gauge Commission adopted Brunel's gauge as the standard, then bespoke wheelsets would not have been required. In all, the Gauge Commission's decision was down to first cost. The same had already been applied to canals, leading to the bizarre 'narrowboat', and ultimately ensuring their demise as commercial carriers; and to the early two-lane motorways, which are currently costing more than their original construction did in widening schemes. There must be many more schemes where the future has been mortgaged for short-term benefit. I personally believe that it is becoming more, rather than less prevalent. All true, and I agree completely that the penny pinching that led to the current UK loading gauge was mistaken and has cost dearly for providing more above the sole bar capacity. If you were arguing that case, I’d agree without hesitation. But I’m still struggling to understand why a broader track gauge would have, in and of itself, given rise to better performance, beyond just giving extra space for engineers to use (which in reality takes us back to loading gauge). Given the speeds and powers reached using Standard gauge, not to mention some of what’s been achieved on narrow gauge systems, I don’t see track gauge having been a fundamental constraint on speed or power. I find it telling that looking across world systems, there aren’t examples from broad gauge operators that show significant advantages in either speed or haulage on those systems, while Japan found standard gauge plenty wide enough for the Shinkansen despite starting with a clean slate having decided to build a wholly new network. |
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Post by billbedford on Jan 5, 2021 10:52:21 GMT
No scientific knowledge is required. You only need look at the development of road motors to observe that larger motor lorries have a broader track than smaller ones. This is not a co-incidence. Stephenson's gauge is not unlike the Motion Picture Academy's frame rate. Set in stone by circumstances which no longer prevail. Perhaps you would like to expand on all the advantages Indian railways, with their 5'6" gauge, have over UK ones? |
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Post by class411 on Jan 5, 2021 11:14:55 GMT
This thread is now way off topic.
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Post by brigham on Jan 5, 2021 17:21:39 GMT
As well as boring...
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Post by Chris M on Jan 5, 2021 17:32:30 GMT
That is a matter of personal preference. The discussion is off topic but not without interest so a passing mod may wish to split the discussions of gauge and power. |
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Post by zbang on Jan 5, 2021 18:06:50 GMT
But I’m still struggling to understand why a broader track gauge would have, in and of itself, given rise to better performance, beyond just giving extra space for engineers to use (which in reality takes us back to loading gauge). Given the speeds and powers reached using Standard gauge, not to mention some of what’s been achieved on narrow gauge systems, I don’t see track gauge having been a fundamental constraint on speed or power. Exactly. Also consider that if the Underground (or any rail project around London) were to be built today, it would be in context of existing rail, and that highly suggest using the same gauge as most other lines.
OTOH, even if there were no existing railways in the area, it would still be advantageous to build using national standard components, if nothing else for cost reasons. There are really no reasons for an urban transit system to diverge from those existing standards.
Back to "how would you power it?" I'd guess 1500-2500v DC via overhead wire, high enough that supply points can be somewhat separated, low enough that the power electronics aren't difficult and distribution clearances aren't great. DC to avoid the large single-phase loads on the power grid, which grid operators "dislike", and to somewhat simplify the train's converters (also DC makes energy recovery from regenerative breaking easier).
AC distribution moves the DC conversion step from track-side onto the train, may involve on-train transformers which take space and weight, and hit the single-phase issue. For urban systems, where it's not difficult to have supply points closer than 10 miles, widely-separated supply points aren't an issue. And for the widely-separated supply to make a difference, the voltage needs to be a good deal higher than it would for DC, which gets back to transformers on the train, taller insulators (underground!), and generally greater clearances.
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class411
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Post by class411 on Jan 5, 2021 18:16:37 GMT
But I’m still struggling to understand why a broader track gauge would have, in and of itself, given rise to better performance, beyond just giving extra space for engineers to use (which in reality takes us back to loading gauge). Given the speeds and powers reached using Standard gauge, not to mention some of what’s been achieved on narrow gauge systems, I don’t see track gauge having been a fundamental constraint on speed or power. Exactly. Also consider that if the Underground (or any rail project around London) were to be built today, it would be in context of existing rail, and that highly suggest using the same gauge as most other lines.
OTOH, even if there were no existing railways in the area, it would still be advantageous to build using national standard components, if nothing else for cost reasons. There are really no reasons for an urban transit system to diverge from those existing standards. Back to "how would you power it?" I'd guess 1500-2500v DC via overhead wire, high enough that supply points can be somewhat separated, low enough that the power electronics aren't difficult and distribution clearances aren't great. DC to avoid the large single-phase loads on the power grid, which grid operators "dislike", and to somewhat simplify the train's converters (also DC makes energy recovery from regenerative breaking easier). AC distribution moves the DC conversion step from track-side onto the train, may involve on-train transformers which take space and weight, and hit the single-phase issue. For urban systems, where it's not difficult to have supply points closer than 10 miles, widely-separated supply points aren't an issue. And for the widely-separated supply to make a difference, the voltage needs to be a good deal higher than it would for DC, which gets back to transformers on the train, taller insulators (underground!), and generally greater clearances.
I suspect that would be the most important point if DC were selected. |
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Post by brigham on Jan 5, 2021 19:53:34 GMT
Curiously, the Adkins-Lewis system mentioned earlier is automatically regenerative.
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Post by rincew1nd on Jan 5, 2021 21:27:00 GMT
This thread is now way off topic. Nobody is making you read it. |
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Post by philthetube on Jan 6, 2021 1:18:33 GMT
But would the underground have been built to a bigger gauge, the tube lines were not built to the loading gauge of main line railways and building tubes to Brunel's gauge would have been both expensive and difficult in the 1800's, I suspect that a narrower gauge would have resulted, possibly narrower than we have now.
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Post by brigham on Jan 6, 2021 8:43:36 GMT
I believe the gauge of the first tube was 2'6", which would be appropriate, given the diminutive bore.
A good job the later tubes didn't follow that particular dimension, or we would have had another 'legacy' impediment.
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Post by Chris M on Jan 6, 2021 12:51:04 GMT
The Tower Subway was 2ft 6in gauge in a 6ft 7 3⁄4 in bore.
The "first tube" title though is usually given to the City and South London Railway, which used standard gauge track in 10ft 2in diameter tunnels (the Stockwell extension used 10ft 6in tunnels)
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Post by revupminster on Jan 6, 2021 14:44:42 GMT
Glasgow subway 4ft. that could have prevailed.
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Post by brigham on Jan 7, 2021 9:04:27 GMT
Glasgow subway 4ft. that could have prevailed. ...along with the cable haulage. |
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Post by selbiehouse on Jan 7, 2021 13:13:42 GMT
If the Underground was built today, what ever form of traction was used, it would not have to follow the main roads as was the case with the early tube lines. There would be no instances of stations with one line being directly below the other such as St. Pauls.
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Post by Chris M on Jan 7, 2021 13:23:07 GMT
Are you sure there would be no vertically-oriented stations? The Jubilee line platforms at Westminster are arranged in this manner.
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Post by quex on Jan 7, 2021 14:01:52 GMT
If the Underground was built today, what ever form of traction was used, it would not have to follow the main roads as was the case with the early tube lines. There would be no instances of stations with one line being directly below the other such as St. Pauls. I wouldn't say no instances, as the Jubilee line at Westminster also has stacked platforms for "site reasons". But the requirement would be much reduced!
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