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Paul Terry · July 10th 06, 09:39 AM posted to uk.transport.london

In message . com,
writes

This is something that's always puzzled me - why does the Rotherhithe
Tunnel change direction?

To stop horses bolting ...

Surely, when it was being built, it would
have been cheaper and easier to just go in a straight line?

It was designed primarily with horse-drawn vehicles in mind
(construction started in 1904). These needed long, gentle inclines
either side, and the only space to build such long approaches and avoid
the many docks in the area was almost parallel to the river (even so a
lot of house demolition was necessary). They were constructed using the
relatively cheap cut-and-cover system.

Once down to final depth, the central part of the tunnel (the only part
needing expensive boring) crosses the river more directly, although
still a little obliquely, because the object was to connect the docks on
the south side of the river with those a little further downstream on
the northern side. The result is the characteristic zig-zag of the
tunnel.

The sharp bends wouldn't have been a problem for horse-drawn vehicles,
of course - in fact, they were deliberate because they prevented horses
seeing the light at the other end of the tunnel too soon and thus
possibly bolting.

--
Paul Terry