"Paul Terry" wrote in message

In message ,
writes

Space for the overhead line isn't the problem. Single deck trams are
much taller than tube trains.

There's quite a bit of clearance above the height of a tube train:

http://www.flickr.com/photos/richard...s/z/in/photost
ream/

In fact, at one stage BR class 503s from Merseyside were going to be
used on the line. Here's a rare picture of clearance trials:

http://www.gscalecentral.co.uk/f/dow...?file=1;127888

However, the length of the 503s proved to be a problem, as there is a
tight S-bend in the tunnel, hence the adoption of tube stock (plus,
the aluminium-bodied stock was much better able to cope with salt
spray on the pier).

But they haven't used aluminium-bodied tube stock on the IoW. I seem to
remember reading that these might have more bimetallic corrosion
problems than steel-bodied stock, which is why they still have some of
the last steel-bodied LU stock.