Some of the worst accidents have been when a horse is heading for a fence and at the last second veers right or left and ejects the driver straight into the fence or the wall.
As far as a runaway, just like riding you will never stop a horse by pulling on both reins at the same time. I have never been on a runaway vehicle but I would like to think that pulling on one rein, making smaller and smaller circles might work. I would then try to see-saw if circles were not working or there was no room. I also fully believe that the driver of the horse has a responsibility to stay with the horse as long as possible and go down with the ship!
When my horse spooks I give the horse somewhere to go when he gets scared. My first reaction is to grab on tight to the reins, which. I know isn't the best, but it is what I do, a habit that is not going to change now. BUT then I release almost as fast as I grab them. It gives Pilgrim a place to go, not to be all confined and held back in a panic state. Usually if I release and guide him in a direction I want him to go, the spook is ended immediatly. I know the time a mama turkey and her 8 babies flew up right in his face, if I had held the reins tight it would have been curtains. I loosened my reins right away, by that time the birds were gone and we went on down the road. I don't know who was more startled me or Pilgrim.
The best time to plant a tree was 20 years ago, the second best time is today.