When I'm driving the car which is not an automatic, I drive one-handed most of the time. I don't know if I use both hands when driving the van, which is an automatic. I'd have to drive for awhile while thinking about what feels natural to figure it out.
“There are two novels that can change a bookish fourteen-year old’s life: The Lord of the Rings and Atlas Shrugged. One is a childish fantasy that often engenders a lifelong obsession with its unbelievable heroes, leading to an emotionally stunted, socially crippled adulthood, unable to deal with the real world. The other, of course, involves orcs.” ~ John Rogers
It varies for me. I drive a manual. Driving through town, and at a more aggressive posture: usually one hand on the top of the steering wheel. Cruising on the highway or with low traffic/minimal turns: usually one hand on the bottom.
If I have a boner, sometimes I use it... hands free.