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# Watch A Semi Truck Get Knocked Over By Nothing But The Wind On The Highway

As someone who is already terrified of the size and momentum of semi trucks while driving, seeing this video of one getting blown over by nothing but the wind while barreling down the highway isn’t helping my irrational fears.

The video was uploaded to YouTube by Isaac Frame a few days ago and posted to Reddit showing the truck getting blown over by winds claimed to be over 80 miles per hour on Interstate 25:

This article from the Denver Post shows images of wind damage across the state from last week, including two images of other semi trucks seemingly blown over on their side. In other images, trees are uprooted and homes are destroyed.

It’s unclear whether anyone was injured in the incident, but luckily nothing else was directly in the path of the truck when it flipped. This is also a good time to remind everyone not to tailgate.

Via Digg

Staff Writer, Jalopnik

### DISCUSSION

Because I’m a bit of a geek when it comes to air, pressure and force calculations, I tried to run a bit of maths on this but it’s actually hugely complicated to model in reality.

Assuming this truck isn’t at some strange altitude, the psi on the side is really low - just 0.11psi. However, the huge surface area (I worked with 45m2) means that there is nearly 4 tonnes acting on the trailer (somewhere - depends on CoG of course!), assuming a 90 degree crosswind. (Very simplified)

However, this doesn’t take into account the low pressure area close in to the side of the trailer from the forward motion, nor the fact that even a box will act as a (really bad) aerofoil and there will be a low pressure/turbulent area on the other side.

So.... engineering question....

Why don’t semi trailers have pressure relief valves (either manual flaps or automatic ones, zipped windows on canvas-sided ones) that can be used when the wind gets over a defined limit?

I appreciate that the wind would have to go through the cargo as well, so you’d have to leave some space where your pressure relief system (i.e. fancily-named holes) goes but it’s got to be cheaper than tipping the entire truck and would allow it to operate safely in all wind conditions.

Airliners have pressure relief systems in both directions to stop them bursting like an over-inflated balloon in the climb if the outflow valves misbehave and, equally, to stop them being crushed like a sunk submarine if the same happens in the descent.

If it was that easy, it would have been done, I know. Just wondering why a small amount of cargo space isn’t given up to pressure relief, as some areas in floors of skyscrapers are.

Anyone know?

(This accident, which happens every other week in winter near where I live, is the bane of my existence when I’m not working abroad. Shuts the bridge down for a day. The truck was blown across the reservation (!) onto the right hand side of the road - Edinburgh, UK)