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Post by stuartroy on May 15, 2017 15:27:24 GMT
At Chancery Lane and St Pauls the platforms are "stacked" one above the other. It's well known that this was done in order to keep the tunnels under streets rather than under buildings.
I understand (and I'm not currently able to verify this first hand, being 500 miles away) that at Chancery Lane the Eastbound is on top, but at St Pauls the Westbound is on top.
1. Is this correct?
2. Does anyone know why (historically) it was done in this seemingly perverse manner with a cross over of depths between stations?
3. If the point was indeed to keep tunnels beneath streets, then does the changeover not defeat the purpose, given that at some point between the stations the two tunnels must be side by side?
4. If the answer to (3) is that the road is wide enough for two running tunnels, but not running plus station tunnels, question (2) still stands, and does anyone know, geographically, where the point in the street is where the two tunnels cross over depths?
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Post by norbitonflyer on May 15, 2017 16:23:40 GMT
At Chancery Lane and St Pauls the platforms are "stacked" one above the other. It's well known that this was done in order to keep the tunnels under streets rather than under buildings. I understand (and I'm not currently able to verify this first hand, being 500 miles away) that at Chancery Lane the Eastbound is on top, but at St Pauls the Westbound is on top. 1. Is this correct? Quite correct 2. Does anyone know why (historically) it was done in this seemingly perverse manner with a cross over of depths between stations? 3. If the point was indeed to keep tunnels beneath streets, then does the changeover not defeat the purpose, given that at some point between the stations the two tunnels must be side by side? 4. If the answer to (3) is that the road is wide enough for two running tunnels, but not running plus station tunnels, question (2) still stands, and does anyone know, geographically, where the point in the street is where the two tunnels cross over depths? I understand the answer to (4) is roughly where the route passes under the Fleet Valley, and that is probably the clue to the answer. (The highest land in the City is traditionally at Panyer Alley, right next to St Pauls station - as declared on the plaque on the wall of Café Nero,  which is probably why the cathedral was built there, but because of recent boundary changes Chancery Lane station is now in the City, and is slightly higher) Central Line stations were always built at as shallow a level as possible, to reduce the number of stairs or depth of lift shafts required (escalators came later of course), so despite being on hills it is not very deep under ground at the two stations, and therefore above sea level. However, in between, it has to pass under the Fleet Valley which is close to sea level, and climb back up the other side. I assume the reason the platform facing away from the dip is the lower one at both stations is to make the uphill gradients gentler. The point where they are side by side is presumably at the bottom of the dip. The Thameslink route runs alongside the Fleet River, at about the same level. As that was there first (opened in the 1860s) the Central Line also had to pass under that Longer explanation here |
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Post by crusty54 on May 15, 2017 19:05:31 GMT
In the past railway companies had to buy any land that was above an Underground line.
This is why the tunnels run above each other.
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rincew1nd
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Post by rincew1nd on May 15, 2017 19:38:45 GMT
There is an old thread on this subject here |
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Post by stuartroy on May 15, 2017 20:29:14 GMT
Thanks both for the current answer and for the link to the old one - I had tried a search but obviously didn't go quite far enough back!
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rincew1nd
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Post by rincew1nd on May 15, 2017 20:37:20 GMT
Thanks both for the current answer and for the link to the old one - I had tried a search but obviously didn't go quite far enough back! It's a thread title that has stuck in my mind for some reason, which helped me finding it. |
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Chris M
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Post by Chris M on May 15, 2017 20:41:24 GMT
Thanks both for the current answer and for the link to the old one - I had tried a search but obviously didn't go quite far enough back! It's a thread title that has stuck in my mind for some reason, which helped me finding it. And my head! |
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Post by mikebuzz on May 25, 2017 12:12:11 GMT
The tunnels dipped between stations to help with acceleration/deceleration.
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