Ad absurdum per aspera
I strongly suspect that there are also cases where *incorrect* use of the seat belt is a significant factor in causing injury or rest.
In the days before inertia reel belts it was *very* easy to wear a belt uselessly - even harmfully - slack.
A properly fitted lap strap is designed to hold the plevis securely to the seat; a slack one can cause all sorts of internal abdominal injuries in a crash.
Similarly, the chest strap is intended to hold the shoulder in place, rather than strangle its user.
Full racing harnesses are a tad over the top for most road cars, where the person occupying any particular seat may be a significantly different size from one journey to the next, but thought should be given to proper use of any available adjustments (such as the height of the shoulder mounting in some cars) and especially to appropriate use of child seats and booster cushions.
When I first took a friend and her young daughter on a trip in my present car they brought a booster cushion. I checked its instructions and fitted it as directed (which, remarkably enough, is how I would have fitted it in the absence of any instructions). For some reason, the mother thought I had got it wrong, and altered it - but the lbutt knew better and agreed with the vehicle commander, so it was altered back.
