On Fri, 11 Nov 2011 22:36:54 -0000, "Paul Scott"
wrote:

"Charles Ellson" wrote in message
news
On Fri, 11 Nov 2011 08:35:12 -0800 (PST), allantracy

To that end, perhaps Overground services from Euston could reverse and
continue in an Amersham direction.

You can't run 3rd-rail stock on the Met.

Not an insurmountable issue though, as seen on the Bakerloo and District,
and the new S stock has apparently been built to allow use on the raised
third rail supply voltage that NR are about to provide around London...

Compatibility is not inevitably a reversable function. The shared
sections all involve some re-arrangement of the power supply and/or
signalling systems. You can e.g. send LU and NR electric stock into
Richmond but neither can take the wrong direction at Gunnersbury as
one requires power between the 3rd and 4th rails and the other
requires the power supply between the 3rd rail and one running rail.
Normal LU signalling is not intended to have traction currents flowing
in the running rails.