On 28 Jul 2008 19:33:58 GMT, Adrian wrote:

Umm, you'd prefer the bridge took more damage?

I'd prefer less damage was done to any passengers. I think this one
was fortunate because it was a rail replacement service, which people
tend to avoid if there's any other option so it probably had three
passengers and a dog on board.

Whatever happens, the front few rows of passengers aren't going to be
laughing and joking about it. If the top of the roof collapses
progressively, instead of just sliding back, then it's going to come down
as well as up. Oh, and they're chewing bridge, of course.

As opposed to that bus, where (if there were any) passengers
throughout the top deck would have had their heads knocked off?

So the only real question is what happens further back on the top deck.
Look at the photo - there's no risk (other than by flying glass) to
anybody else on that deck from the roof sliding backwards - because it's
remained at fundamentally the same level. Yes, it's dropped down
slightly, as it's cantilevered backwards on the pillars, but that's not
going to do TOO much harm.

It's dropped down by the whole height of the main pane of the windows.
If I was in a bus involved in such a collision and hadn't seen what
was coming and ducked, it'd certainly have taken my head off.

A more rigidly constructed bus might have flattened the front quarter
of the top deck, but decelerated more quickly (more resistance from a
stronger body) and not flattened the back bit at all.

So - you reinforce the window pillars upstairs. A LOT. They're going to
have to transmit the forces backwards, else they'll just bend again, so
they'll have to be angled. That's going to put a LOT of force into the
rest of the bus structure, and almost certainly do significantly more
damage to the rest of the bus. I'd imagine it's fairly straightforward to
re-roof something such as that - but an impact of that force through a
structure designed to spread the forces and hold the roof on would very
probably write the entire body off.

It is conventional that road vehicles should themselves be damaged in
preference to their passengers. Think crumple-zones. The cost of the
damage is hardly relevant to the issue - that's what you have
insurance for. (If the bus companies are self-insuring, that's their
own choice).

That bus appears to be an older, turn-of-the-century design, with
ribbon glazing and almost no pillars. Would a more modern
rounded-window design with gasket windows and wider pillars (where the
windows don't contribute as much to the structural strength) have
perhaps done better?

Alternatively, perhaps the drivers could consider looking where the ****
they were going? I mean, it's not as if there isn't already a legislated
requirement for the vehicle height to be clearly marked in the driver's
view, and for low bridges to carry height warnings...

This is true, but it's not a reason not to make vehicles more
crashworthy. On the railway, the Pendolino that got smashed at 110 at
Greyrigg showed just how good modern railway body design is - it
survived pretty much intact and was only written off (as I recall)
because of damage to equipment, not because of deformed bodyshells.
Some of that could be applied to the bus and coach industry, surely?
It doesn't need to be *as* good because, in Central London or any
other city, the maximum closing speed is going to be 60mph or so, not
250mph, but it could be a lot better.

Neil

--
Neil Williams
Put my first name before the at to reply.