On Mon, 8 Oct 2007, Paul Scott wrote:

"Abigail Brady" wrote in message
ups.com...

I was pondering a map the other day, and I noted quite how close
Moorgate and Cannon Street are. I guess the city widened lines to
Moorgate are a lost cause due to the planned work at Farringdon, but I
wondered whether it has ever been suggested to extend the Northern City
Line south of Moorgate and link up with the line at Cannon Street,
making Cannon Street into a through station.

Has this ever been suggested?

Yes, about every eighteen months on this group!

Are they any especial difficulties apart from the sheer cost of
tunnelling in EC2. (Bank of England vaults?, I can also imagine the
gradient being a problem)?

Gradient would definitely be an issue

Cannon Street bridge is 7.1 metres above the high water level of the
Thames [1], perhaps less at the ends. The rail deck will be a little above
that - not more than 9 metres, and probably less. It's about 260 metres
from the point where the bridge makes landfall to Cannon Street itself,
where the space occupied by the station ends (ish). If you hollowed out
the existing station and put in a downward-sloping track at a gradient of
1:30 (generally considered the practical maximum, i think), you could drop
8.5 metres in that distance, leaving you at about the level of the river.
You need about four metres over the top of the track for the train (six if
you want OHLE, which we don't). If Cannon Street is four metres or more
above the level of the river, this idea is just about plausible - at least
this far!

In terms of getting to Moorgate, you're then alright, as you have about
650 metres to run, in which space you can dive another 20 metres, which i
think is enough. The problem, of course, is all the buildings and whatnot
in between the two. If you could run under Walbrook and Prince's St,
though, you might be alright. You might need to demolish No 1 Poultry, but
it's a horrible building anyway.

Don't ask me about how it all fits in with the Bank station complex.
Didn't someone say they thought that was plausible?

Lonelytraveller mentioned the Walbrook; i don't know what you'd do about
that either.

When DLR extensions have been suggested in the past it is usually
mentioned that the Bank of England vaults are in the way too!

The vaults thing is a red herring when it comes to the NCL, though - there
have been serious proposals from the time it opened up to the 1960s to
extend it southward, and none of those had any problem with vaults.

The alternative to going to Cannon Street is to stay in deep tunnel, cross
the river, go to underground platforms at London Bridge, and then surface
onto the appropriate tracks east of the station, bypassing Cannon Street
and its spur altogether. Although if you're going to do this, you might as
well take the tunnel west and do something more interesting ...

tom

[1] http://www.the-river-thames.co.uk/bridgeheights.htm

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