In message , at 10:45:45 on Tue, 26 Apr
2011, d remarked:
On Tue, 26 Apr 2011 11:22:27 +0100
Roland Perry wrote:
I don't know. What I do know is that modern road bridges and viaducts to me
seem to be very over engineered given the total weight they'd ever be
expected
to carry. Eg , that M1 viaduct that had a fire underneath.

That's built to carry three lanes of 40 ton HGVs.

Even 3 HGVs only weigh the same as a single locomotive. A rail bridge may have
to carry 2 locomotives plus their trains at the same time.

Huh? I thought you were arguing that a bridge built for a couple of 14
ton buses would be adequate for two 150 ton trains... and now you are
quibbling about a mere couple of hundred tons of loco as well

Rail bridges OTOH seem to be somewhat slender in comparison.

The busway bridge is pretty slender too. Here's someone's picture of it
under construction.

http://mw2.google.com/mw-panoramio/p...m/12999233.jpg

It would be interesting to see how slender it looks with a few hundred tons
of concrete busway on top of it.

I'm sure you can find some photos online. The trackbed isn't going to be
structural (because it's prefabricated blocks laid down) but you should
also compare the size of those beams with the ones under a motorway.

coupled with the fact that it would have provided a useful diversion
route for the ECML.

Single track and non-electrified (ignoring the reverse at Huntingdon for
a moment) does not make a very useful diversion.

If the line had been re-opened electrifying it would have been the only
sensible option unless DMUs were to be run all the way from london or have a
DMU shuttle service from cambridge.

Actually, the proposal was for "railcars", terminating just west of the
Milton Road in Cambridge. The proposers then expected Network Rail's
tooth fairy to reopen and electrify the line across the Milton Road
(level crossing) and onwards towards Cambridge station, with passengers
changing trains to start with.
--
Roland Perry