please empty your brain below
I believe the Chancery Lane/St Pauls anomaly can be explained by looking at what's in between them - the Fleet Valley. The Central Line has to dip under this (and the Thameslink route alongside) and then up the other side to be at a reasonable depth under the rather higher ground where the stations are - there is a plaque outside St Pauls station announcing it as the highest point in the City of London (the highest ground, obviously - many buildings overtop it!)
By having the platforms the way they are, the uphill climb on each side of the dip is made a bit shallower than the downhill drop to it, making it easier for the trains to manage.

It is for a similar reason that the Northern Line through Bank runs back to front - the second tunnel to be dug was lower, and further away from the west side of London Bridge (the span, not the station). The shallower tunnel was used for northbound trains to give them a better chance of making it upm the hill to the King William Street terminus.

The Central line does, in general have its stations at a slightly shallower depth than the running tunnels between stations. This reduced the cost of digging lift (and later escalator) shafts but was primarily a way of saving power by allowing gravity to aid both acceleration and braking. This can be clearly seen on stations further west, where the line is straight. (Holborn is an exceptrion as it was built later)

timbo | 16.03.13 - 8:16 a.m. | #

Isn't there an up escalator to the Jubilee Line platforms at Canning Town? That has been there for some years i.e. since the Jubilee Line extension was built, presumably.

| 16.03.13 - 8:35 a.m. | #

Uber-uber-geek fact:

Of thos two staircases at Greenford, the one in the middle has 51 steps, but the one that replaced the down escalator has 54 steps - even though they both start and finish on the same levels. explain that one!

(well ok, the physical step height is slightly smaller on the one with more steps, obviously...)

geofftech | 16.03.13 - 8:54 a.m. | #

And, of course, Alperton also used to have an escalator that you rode up to the platforms. Now hidden away behind brick ways and closed doors...

Dominic H | 16.03.13 - 9:12 a.m. | #

+1 for Canning Town having escalators up from ticket hall to platforms.

I believe the primary reason for the escalator at Alperton was so it could be used as a test bed for various machine types by the Underground's engineers.

Marc | 16.03.13 - 9:52 a.m. | #

Do you not take an escalator up to the Jubilee Line platforms at West Ham too?

Richard M | 16.03.13 - 10:37 a.m. | #

Off topic, but just spotted you're first place on google search for diamond geezer. Don't know if its been there for ages as usually visit via a favourite, but congrats anyway.

dg writes: Me and the jewellers regularly jostle for first place. But it's nothing new :)

Geo_rich | 16.03.13 - 10:38 a.m. | #

Those escalators at Stratford aren't the originals and were replaced as complete units prior to the Olympics.

Kim | 16.03.13 - 12:20 p.m. | #

Alperton:

http://www.flickr.com/photos/24772733@N05/4880139922/

Stratford:

http://www.flickr.com/photos/24772733@N05/6668262031/

Kim | 16.03.13 - 12:24 p.m. | #

@timbo wrote: 'The shallower tunnel was used for northbound trains to give them a better chance of making it upm the hill to the King William Street terminus.'

Not quite. The original C&SLR tunnels from London Bridge to King William Street were abandoned when the line was extended northwards, and Bank took over as the first station on the north side.
The old tunnels were used during WW2 as a bomb shelter. They were still there in the early 1980s (complete with the markers for the shelterers' bunk beds, and a set of loos at the northern end) when I went on a conducted tour with an industrial archaeology group.

Alan Burkitt-Gray | 16.03.13 - 4:39 p.m. | #

I can't believe there's something I've done and DG hasn't! (ride the Greenford branch)

Actually I've ridden every suburban line in London in both directions (except for Strawberry Hill to Fulwell, and Rickmansworth to Croxley, and Arabfly northbound - no point paying for that)

John | 18.03.13 - 7:34 a.m. | #











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