Where would we be without the good-old wheel? It allows us to travel over hard-packed surfaces like dirt paths and paved roads with ease and speed, and it's been doing a pretty good job of it for thousands of years.
Unfortunately, our friend the wheel has never been a really great performer in mud, snow or water, because these media don't provide a firm enough surface to push against the way solid ground does. The lack of resistance with these surfaces is actually a hindrance to traversing through them.
But over the years, several vehicle makers have come up with a solution that appears -- well, downright screwy. In fact, it is screwy. These contraptions move through semi-viscous material like snow and mud in just the way a screw is propelled through wood.
If you're a faithful HowStuffWorks.com reader, then you know the "drill:" read the next page to learn about screw-drive vehicle design.