In message , John Rowland
writes

On http://www.crossrail.co.uk , the posters which appear at the consultation
are downloadable as PDFs. In one of them (Central London Stations) most of
the physical obstructions that Crossrail has to avoid are marked. Between
Liverpool Street and Whitechapel there are two tunnels marked "Services" and
one marked "Obs." Sice they are all about 30 metres down, I'd be fascinated
to know what they are. Presumably Obs stands for obsolete? (The Post Office
Tube, although obsolete, is elsewhere.)

Just a guess, but could it be one of the tunnels built by Halcrow for
the GPO telecommunications network in the 1950s? The original system was
8 miles long and involved seriously big tunnels (16.5 foot diameter) at
deep level. According to "London Under London" one of these runs east
via the Moorgate exchange to the Houndsditch Exchange close to Liverpool
Street, then NE to Bishopsgate and Bethnal Green - so CrossRail would
need to cross it at some point.

I don't know that these tunnels are technically obsolete, but it could
well be that in the digital age cables have been re-routed so there is
no need to keep up the costly maintenance of tunnelling on that sort of
scale. In any case, their original purpose (to maintain communications
after nuclear attack) was never properly thought through, and is now
somewhat redundant.

--
Paul Terry