I recently drove an 8 1/2 hour trip to MA. from MD. Actually, my wife did most of the driving and I was navigator. Just sitting in one position for hours (we would stop every 3 hrs or so to 'stretch', gas up, or eat) would make my whole side of my leg from my feet to my hip, go numb. My feet began terrible burning, and when I got out, the pain was intense. Walked like a drunken sailor until things 'worked the kinks out'. Needed at least 15-30 mins to get to the point where I could get back in the car for the next 3 hrs. Usually I can drive for the same period (3hrs) until I need a break. The constant accelerator/brake action keeps my feet active, but they still go numb after a while. Cruise control lets me move my feet around and stretch them while driving on the interstates.