Okay, I'm going to try this link thingy again :-)
Traveling with Your Cat OB and I did lots of traveling with our cats and they do settle down fairly quickly. Once we got out of traffic we would let them out of their carriers and they would snuggle up with each other, or find a hidey hole in the car. If you are concerned about medications there are some good holistic meds out there for cats.
When that hiddyhole is curled up on my accelerator foot then there is an issue ;p