Here's what happens when you drive a 12-ton bus across a 10-ton bridge

Originally published at:


@frauenfelder no video/linky…

Possibly this…

Bridge name is the same but in Arkansas

ETA and the bus is 35 tons with a 10 ton limit on the bridge… I am impressed with the engineering.

ETA More @orenwolf as you usually respond. Mark has no link to anything.


Also, why the right justifcation? Keyboard acted up, and @frauenfelder abandoned post?

This particular bus may or may not be 35 tons; it wasn’t weighed; they simply stated these buses could weigh up to 35 tons.

Thanks for the link @TobinL; much appreciated!


That coach weighs around 12 tons. The bridge limit is 10 ton but there will be a factor of ignorance or a large safety margin e.g. the bridge can cope with 18 tons. A non story. Though it is interesting to see the bridge stress and strain.

The comments are filled with treasures like this. Every hillbilly is apparently a structural engineer, assuring us how safe it is. (Some masculine reflex to “being told what to do”; “I don’t want to wear a jacket, Mom! I don’t care if it’s cold outside!”)

The quite obvious sagging is “a non story”, I guess, because the bridge didn’t actually collapse.

How can he possibly know exactly how much the coach weighs? Theyll weigh between 10-16.5 tons empty, 15-22 tons full.

Why do I know this guy also voted for Trump, is a climate denier, and (if pushed to make a statement) will allow that “sure, something’s fishy about 9-11.”


Don’t you think that’s a very loose definition of “knowledge”, in particular in the context of scolding others for their ignorance?


Anyone here not seen the film of ‘Galloping Gertie’?

If that bridge is 70 years old, then it must have been put up in the forties, same decade as Gertie. If it fails, it will probably not fail for the same reasons as Gertie. But it shows that the reason bridges fail is not the static weight (though doubtless that would do, if you tried hard enough). Here, the bus is driving a wave ahead of it, which means it is effectively driving uphill. All that extra energy from driving uphill must be going into the bridge structure. Where does it go then? If the bridge had dampers and dashpots to absorb it, then this would be okay. But it hasn’t, so most of the energy must go into the supports where metal meets concrete, and the recoil after the bus has passed may shear the joint upwards, where it has not been designed to resist stress.

The 10 ton limit is probably for 10 tons spread evenly and moving very slowly. The actual limit for moving faster is not an easy calculation, but provided you are not like that fool, racing to get across before it falls using Wile E Coyote physics, then all might be well.

A bit of that energy-generating piezo road ought to tell whether things are too heavy before they get to the bridge.


Weight limits aren’t just about risk of collapse.One bus can go over, no problem, but it causes a lot of extra wear on the structure. At some point that bridge will have to be closed for extensive repair, but by then those buses will be long gone and someone else will be stuck with the bill. (assuming there is money available).


I see no video at all.


Thank god for safety factors.


Thank god building codes & standards for safety factors.


…that’s how tiny the bridge is now. Completely collapsed.


Maybe an IoT scale, a licence plate reader and an automatic ticket printer would solve the problem that signs and common decency can’t solve. Too bad the bus drivers cannot take responsibility for sharing the commons, but it’s not the first time that’s ever happened.



Wow! An invisible video! Amazing!

Or does the lack of a video mean nothing happened?

This story says it was not a 12-ton bus, but a 35-ton bus, which is more than triple the capacity of the bridge:


Don’t you see, Boundegar? The bridge was inside you all along.


You can see

Can i though?

Narrator: He could not


Seems like a solution solved by parking a sheriff deputy on the far side of the bridge and handing out tickets.


I bet like a lot of things it’s fail rating is 3x+ more than its working rating. That is one can drive things across all day long at its working rating and it will be fine. You can drive things across at its fail rating a few times.

At least that is the case with HPA tanks. To get them re-certified every 5 years or so, they pump them up to 2x or 3x (I forget which) their normal operating pressure and see if they fail. Though the criticism of some users is that a tank could go forever at its operating pressure and only when you overfill does it fail. But how else do you test safety?


Anybody know which domains I need to consider enabling scripts from to see the video?


“Yeah, so what if we were playing Russian Roulette? Nobody died!”

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