I can relate to your story...shortly after I came to Reno, a ladder fell of, onto the freeway. A good Samaritan, who was trying to remove this hazard from the roadway, was struck and killed. Point taken- I've always made sure my ladders were well attached.
It's a real riddle, just how do you attach a ladder in a manner that is fast, easy, as well as secure. Not all of us have the $$$$ to get some sort of fancy ladder rack.
In my earliest days in the trade, my "safety" was a hasp, to which I attached a steel cable and a padlock. There were, I admit, a few times where an unexpected bump in the road led to the ladder breaking free- but it stayed attached to the turck, and followed me over to the shoulder. Nothing hurt but my pride!
My current truck also doesn't lend itslf to your usual ladder rack. So, this time around, I have place strut across the top, and attach ladders with modified strut clamps. This arrangement also works for other large loads.
