TheOneKEA wrote:

Graeme Wall wrote:
(unsnip)
John B wrote:

That would be the cause of the disruptive alterations. It's generally
frowned upon to build a new bridge over an operating motorway...

???

What about all those motorway junctions that acquired extra bridges when
they were roundaboutized above the motorway?

Easy enough, prefabricate the thing alongside, close the road overnight and
swing the thing into position when ready. Not exactly rocket science.

Ah, but no one has yet mentioned the fact that the M40 crosses the
formation _on_the_level_. The A40 does not, and still has the bridge
abutments to prove it, but the M40 apparently foes right over the
formation, and too closely to the A40 to allow for easy gradients.

So unless a horrific gradient was contemplated, the M40 would have to
be lowered to the same level as the A40, which would cost $WAY_TOO_MUCH.

That's a very strange conclusion!

Obviously the new track would be higher than the old formation, to
enable it to bridge both roads easily. Is there any good reason why
cranes could not lift the prefabricated deck into position overnight (or
even over several nights)?

--
Aidan Stanger
http://www.bettercrossrail.co.uk