In message , at 17:37:05 on
Wed, 10 Oct 2012, Basil Jet remarked:
Especially as I've taken pains to explain the tunnel was built in the
middle of nowhere (at the time) and the ferry connected existing
built-up areas.

Why was it built in Dartford though, when a tunnel from Gravesend to
Tilbury would fit in much better with the pre-M25 road network... or
was it because the M25 was already planned when the first tunnel was dug.

It might be lack of land on the banks in those places to construct the
tunnel mouths and toll booths, or a desire to send whatever traffic it
was they expected "round the bypass" rather than through the centre.

Both probably.
--
Roland Perry