One of the most painful parts of a car ride for me is the swaying back and forth that the torso does. You are tensing the body in order to hold it upright. It makes me incredibly sore. So I tend to agree with Aussie that an elastic brace might be a good idea. Something like maybe one of these?
http://store.orthoathletic.com/merch...ct_Code=31-560 This is just an example and may not be the right one for you.
Billye