exactly how do these crashes work?

Link

I'm looking at this vid and the thing going through my mind is how does this work? Do the polls go down depending on the weight of the vehicle? Is there some official scanner? Or are these people knowingly trying to get somewhere where they don't belong?

That a stupid device and I hope I never encounter them when I am driving.kulmiye

It's not like they're hidden and there are signs telling you they're theremarkop2003

[QUOTE="kulmiye"]That a stupid device and I hope I never encounter them when I am driving.markop2003