On Sun, 30 Nov 2008 18:00:27 -0000, "Peter Masson"
wrote:


"Christopher A. Lee" wrote

Of course it made sense to use the existing 4 rail system because
apart from the LBSCR's overhead AC that was what the other London area
lines used. The LNWR electrification was planned in 1907 and opened in
1914, with the Bakerloo linking up a year later.

The original plan was to extend the New Lines from South Hampstead in
deep-level tube to a terminus below Euston. In 1911, before the New Lines
opened, this plan had been abandoned in favour of linking with the Bakerloo.

OK.

Even what was done was a major effort, quadrupling the track out to
Watford with other major engineering works.

The LSWR 3 rail system was planned later with the first section
opening in 1915.

Did the LSWR ever consider using the 4 rail system? The first LSWR line to
be electrified (apart from the isolated Waterloo & City) was the route
between Waterloo and Wimbledon, via East Putney, including the section
between East Putney and Wimbledon which had already been electrified on the
4-rail system for District trains. So this was the first use of a line
adapted to take both 3rd rail and 4th rail trains.

I don't know.

By the time the LSWR electrified there were other systems for
comparison. I believe they had looked at the Liverpool-Southport
electrification before they made up their mind.

I do know that the New York Subway has major electrolytic corrosion
problems on their elevated sections, which are like continuous girder
bridges.

I've never read of the third rail system having the running rails at a
negative potential on either side of the Atlantic.

Tram and streetcar track did this so the problem has been known for a
very long time.

Perhaps it is because pipes etc were laid under streets and surface
trains had their own right of way. The original Met and Metropolitan
District lines ran cut-and-cover under the streets, as did the tubes
because of easement issues. And of course the latter tunnels were
lined with cast iron segments.

Peter