Huey is always in a car seat when riding with me alone. Rarely, on extended trips when dh is driving, I will hold him in my lap for a bit, but I do understand the dangers of this. I have a snoozer-type elevated seat for Huey and it has a little attached tether, but I know for a fact that it would take very little for that tether to break/pull loose, so I don't use it. I DO wrap his leash around the seat of the car & lodge it firmly under the headrest, leaving turning around/lying down room for Huey but short enough that he cannot be thrown in to the windshield or floor. His leash is always attached to a well-fitting harness that distributes pressure evenly across his torso.
He really doesn't seem to like this seat as well as he did his old cheap, flimsy basket-type seat that finally self destructed. I think he felt safer all tucked down in that as opposed to the much more shallow snoozer.
There was a thread in the past that was very informative about car seat safety for pets:
http://www.yorkietalk.com/forums/yor...ar-travel.html