Ian Jelf wrote:

I was about to mention Charleroi. A perfect example of the original
point. It's the equivalent of having something on the scale of the
Tyne & Wear Metro inserted into somewhere like Reading.

It was largely built, as Boltar says, for political reasons. The
Flemish North had a light metro (as the Walloons saw it, anyway) in
Antwerp, so the Walloon South had to have something the same.

It's a long trine since I've been but the **vastly** over engineered
and little used infrastructure was incredible. (Mind you, Gent
built an extension for a proposed housing area that never
materialised and which terminated in a no-mans-land beneath a
motorway for years. I understand that it's been abandoned now.)

Closer to home, Sheffield's tram network has a branch to serve a high-rise
housing estate which was demolished while the tramway was under
construction.
Speaking of underused infrastructure in Sheffield, what happened here?
http://maps.google.co.uk/maps?hl=en&...06866&t=k&z=18

And of course, even closer to home we have the Finsbury Park to Highgate
line, electrified but never served by an electric passenger train.