I remember this thing happening as a child ... luckily I was just a bus passenger. The caravan was taken by air pressure and tipped over right in front of the bus as the bus was passing the caravan.

Now, that didn't make completely sense, why would it happen in front of the bus if it was the bus overtaking the caravan? I was a small child, it's like 35 years ago, and the details aren't that clear anymore. Perhaps the bus driver applied the breaks as soon as he saw something was not going very well. Or, more likely, it wasn't the bus but some other vehicle overtaking the caravan causing it to flip over.