Travelling with dogs

How many times have you been driving along and see a dog riding in the back of a pickup truck? Maybe it's just me, but visions of what could happen to that dog run through my head immediately. I know the driver must be confident that the dog won't jump out at high speeds or when stopped, but how can you really be sure? Then you have a loose dog in traffic.

And what happens to the dog if there's an accident? Is the dog better off being free to fly through the air to land safely on the ground rather than inside the car unrestrained? Maybe - depends on the speed of impact and what the dog actually lands on, I suppose. Has anyone ever experienced an incident with a free riding dog? Do tell, because I'd like to know.