In message , at 11:47:08 on Mon, 25 Apr
2011, d remarked:

I doubt one designed to carry the weight of 2 buses is significantly
cheaper than one designed to carry 2 or 3 car passenger trains or even
light rail.

Of course not. After all you'd only have to design for two trains at 150
tons each (45ton/car), versus two buses at 14 tons each. Remind me not
to stand under any bridges you've built!

Most of the weight a bridge has to support is its own weight. When you
get into those sorts of tonnages the weight of the vehicle crossing it
becomes only a small percentage of the total weight so the overall structure
of a busway bridge I suspect is not much less than that of a railway bridge.

Let's say 90% of the weight of the bridge is required to keep itself up, and
only 10% is represented by the safe load above it. That would indicate that
a bridge for a 14 ton bus would need to weigh 140 tons. Are you suggesting
you could run a 150 ton train across such a bridge, rather than needing a
1500 ton construction?

You only have to look at how well built most road bridges are to appreciate
this.

That could easily be accomodated with a railway by having single track
with double track at stations.

That's a novel idea - do you know anywhere there's a railway and nature
trail squeezed onto an old railway track, with sufficient crossings that
people can access the trail from both sides of course.

Not on a mainline no. But a number of preserved railways do have that. I
don't know if the rules are different however.

I think a big part of the problem with proposed rail re-openings on this
line have been a result of treating it like a preserved railway, rather than
a service railway.

And 2 busway tracks takes up a shed load more room than even a double
railway line.

Actually not, that's the point - it fits in the same space. Or do you
have some mythical trains that are narrower than a bus, so they can
squeeze through a smaller gap?

Looking at streetview it looks wider.

A bus is narrower than a train, you can't get away from that basic fact. And
if you guide the buses through bridge holes, you can get them side by side
in the same gap as trains. Here's the bridge where the A14 crosses the
track: http://lh5.ggpht.com/_bKS0Ey2ovWg/S0...Juw/lsOI55-V7_
E/P1030018.JPG

And I remember reading that they
had to demolish some structures and cut back the old station platforms
to fit it in on the same route.

They demolished the platforms at Histon Station, but that's probably because
it's the site of a bus stop, not just tracks, http://goo.gl/maps/8rRZ
and they've also raised the ground level there quite a bit. Compare this
picture with today's streetview http://goo.gl/maps/Q6gY

http://www.disused-stations.org.uk/h...11.2005)22.jpg

As the line would run empty most of the day, it's preferable for the
buses to be carting air around than a train. The buses also have a
larger catchment area (the rival rail proposal only covered about half
the guided bus's route, something that's often forgotten).

Are you talking about the actual busway or the entire bus route?

The buses are travelling from Huntingdon to Trumpington, via the centre of
Cambridge. The rail reopening was just St Ives to Chesterton.

If you include normal roads thats an unfair comparison since the buses
can used them whether the busway exists or not and their cost is
zero.

There isn't a direct road between the villages which the busway connects, so
it would be very hard to run a bus in the absence of the busway. The bigger
problem is that those villages won't create enough custom to fill a bus
every 20 minutes, let alone a train.
--
Roland Perry