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#11
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Dodgy gates at finsbury park
On Fri, 13 May 2011 15:31:32 +0100
"Mizter T" wrote: Think it may have lost its crown of the 'misery line' to the Jubilee these days but must say that I do still boggle a little when travelling on it during the high-peak. I don't understand why the trains run so slowly. 20mph seems to be the max in town. B2003 |
#12
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Dodgy gates at finsbury park
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#13
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Dodgy gates at finsbury park
On Fri, 13 May 2011 19:08:45 +0100
Paul Terry wrote: I don't understand why the trains run so slowly. 20mph seems to be the max in town. Faster speeds require a greater distance between trains, so if they ran faster there would be no improvement in frequency (which tends to be the thing that matters for most people). Sure, but they run slowly even when there isn't a train in front for literally miles because you've just waited 10 minutes for one to show up. Even on long sections between kings cross and angel they seem to trundle along at their own leisurely pace. I don't understand why they bothered to spend all that money on new trains in the 90s if theres no improvement in service speed from using them. 15 years is long enough to up the line speed. B2003 |
#14
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Dodgy gates at finsbury park
On Fri, 13 May 2011 15:20:43 +0100
"Paul Scott" wrote: Looks like Boltar has missed about three or four years worth of on and off discussion here explaining exactly what happens at OSIs. My eyes probably glazed over. B2003 |
#15
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Dodgy gates at finsbury park
On 13/05/2011 19:08, Paul Terry wrote:
In message , d writes I don't understand why the trains run so slowly. 20mph seems to be the max in town. Faster speeds require a greater distance between trains, so if they ran faster there would be no improvement in frequency (which tends to be the thing that matters for most people). Once the line is signalled for full ATO, speeds will improve (but even 20mph is twice the average car speed in central London). I thought that they were closer to 35 miles. I know that the Northern Line is 35 miles in central London. |
#17
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Dodgy gates at Finsbury park
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#18
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Dodgy gates at Finsbury park
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#19
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Dodgy gates at Finsbury park
In article ,
() wrote: *From:* *Date:* Sun, 15 May 2011 05:19:48 -0500 In article , d () wrote: *From:* d *Date:* Sat, 14 May 2011 15:23:01 +0000 (UTC) On Fri, 13 May 2011 19:08:45 +0100 Paul Terry wrote: I don't understand why the trains run so slowly. 20mph seems to be the max in town. Faster speeds require a greater distance between trains, so if they ran faster there would be no improvement in frequency (which tends to be the thing that matters for most people). Sure, but they run slowly even when there isn't a train in front for literally miles because you've just waited 10 minutes for one to show up. Even on long sections between kings cross and angel they seem to trundle along at their own leisurely pace. I don't understand why they bothered to spend all that money on new trains in the 90s if theres no improvement in service speed from using them. 15 years is long enough to up the line speed. B2003 The speed limit on the City branch is 35mph (30mph on the CX branch) Apart from a couple of short level pieces and the very short dip after City Road and Kings Cross stations, line between Kings Cross and Angel SB is fairly steep uphill all the way. When motoring, the train cannot even reach the maximum 35mph allowed (a bit like running between Camden Town and Bull & Bush). The 95 stock were slugged on arrival to prevent them being able to run faster than the 59 stock then on the line. This was supposed to be removed when all the 59 stock had gone. This was then changed to "it will be removed when the new signalling comes in". Apart from the gradient, there are several things which limit how fast a train can run or can cause delays to a train and one of these is the infrastructure. There are presently many places on the older lines (where the tunnels generally followed the layout of the road above) that force speed restrictions to be in place. On the Northern line, this is especially noticeable between Kennington and Moorgate, with permanent speed restrictions of as little as 15mph. Short of major tunnel realignment (like they did to the SB C&SLRly through the old siding at Elephant & Castle), there's not much can be done about that. Another thing that can slow a train down is the length of the signal section (the distance a train must travel before a signal behind it can clear and let the following train proceed). These vary immensely, from as little as around 100 feet to over 3200 feet. At Highgate SB, the section is a long one and the station starter will not clear until the train in front has travelled the equivalent distance from West Finchley to Woodside Park. As a consequence, there is usually a delay at Highgate SB if one train is directly following another. Clapham North NB is another pinch point when following a train, as the starter will not clear until the train ahead has arrived in Stockwell platform. Again, this causes a delay to the train in the platform. Whilst these delays might be short, they add up over the line. Where there is the equivalent delay between stations, a driver, knowing they are following a train and can see the red signal ahead, will normally drive at a slower speed in order to give the train ahead time to clear the section and thus avoid actually stopping at the signal. This also means that the driver doesn't then have to make a P.A. within 30 seconds of the train stopping - at least that way the train is still moving, even if it's only at a few mph. This is something where new signalling can make a difference because the sections can be much shorter because the speed of the train will automatically be reduced as necessary to still retain the braking distance. This will mean that the frequency can be improved because the trains can get closer together if required. Roger " behind it can clear and let the following train proceed). These vary immensely, from as little as around 100 feet to over 3200 feet." Sorry, slight typo" - that should have read"around 500 feet to over 3200 feet" Roger |
#20
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Dodgy gates at Finsbury park
In article , (Clive
D. W. Feather) wrote: *From:* "Clive D. W. Feather" *Date:* Mon, 16 May 2011 23:10:06 +0100 In message , d wrote: The 95 stock were slugged on arrival to prevent them being able to run faster than the 59 stock then on the line. This was supposed to be removed when all the 59 stock had gone. This was then changed to "it will be removed when the new signalling comes in". I don't understand the logic behind that. Surely they'd want the trains to have the maximum possible performance for when it can be used? eg going up the steep incline from archway to highgate or the long run from east finchley to finchley central? The signalling may have been designed with certain assumptions in (e.g. "a train passing Archway at 5mph won't exceed 20mph at signal XYZ"). Changing the train characteristics could invalidate those assumptions. IIRC there was a collision or derailment near Watford Junction because modern rolling stock invalidated the signalling design assumptions. -- Clive D.W. Feather | Home: Mobile: +44 7973 377646 | Web: http://www.davros.org Please reply to the Reply-To address, which is: Because there's a maximum speed restriction on the line, drivers should never exceed that speed and, as far as I'm aware, excessive overspeed isn't normally taken into account (or wasn't). I suppose the existing signalling could have a "well a driver's never going to be able to get more than x mph" built into it. It used to be taught that a signal was always "placed a safe braking distance" from the train in front, based on train speed, gradient and weight. However, the Holborn crash proved that wrong and to "safe" was dropped and it became "placed a braking distance"! Normally the only time there isn't the "safe" braking distance is at station starters that have a short overlap and, in theory at least, the rear of the train in front could be just 100 feet or so away from the red starter. (In practice, this would only happen if the train in front has stopped after just clearing the overlap, rather than stopping at the next signal). As a consequence, drivers non-stopping a station where trains normally stop have to reduce their speed to 5mph at the starter. If the starter's green, there will normally be a sufficient braking distance. However, the idea is that drivers will always approach the starter as if is at danger, rather than running full speed only to find it remains red and they go past the red signal at speed with potentially serious consequences. I suppose that this could be another reason for not allowing the trains to run at their maximum power, so that trains can't approach a station any faster than they can at the moment, but I still can't see it as a real reason. Perhaps they're just being cautious, or perhaps it's "tidier" to leave things as they are until the new signalling comes in. The other thing, of course, is that the update has now taken a lot longer than originally planned. Perhaps at the time they thought "Oh well, it'll only be a couple of years by the time everything's finished, we'll wait until then"! Roger |
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