That's basically the old country technique. Driver over them and smash 'em with a hammer...
or rock...
We had black walnuts everywhere on the farm and my dad would take us out in the pickup through the fields to gather them in the fall when they started dropping. We'd dump them on our road (I just can't bring myself to call a 1/4 mile gravel road a "driveway"), drive over them for a couple weeks. You didn't want to take the hulls off by hand because your hands would be stained dark brown for weeks.
After the car tires did the de-hulling, and a couple weeks of autumn sun drying time, then we'd pick up the nuts and start smashing the darned things for baking for my grandmother. She dumped about a gallon of black walnuts in stuff over the course of the year (and we always bit into a shell somewhere in a cookie or cake). And me, I hated them, and now I miss them because that was the taste of grandma's chocolate chip cookies and sprinkled decoratively on her cakes and such. They are definitely an acquired taste IMHO.
Now hickory nuts, on the other hand, those are sublime. But like black walnuts, also a lot of work to get into an even smaller and harder shell for a smaller nut. My dad's favorite cake was hickory nut cake with vanilla frosting smothered in more hickory nuts. He got at least one each fall for his birthday in October.
