Flashy is right, short car rides help the rabbit to get accustomed to car travelling (always depending on each individual rabbit). My bunny hates cars, but has absolutely no fear for ships, he has repeatedly travelled for 12 and 14 hrs. in a ship cabin and was hopping around like a skipper, even with rough seas! The car, though, is a most uncomfortable place for him, not so much for the fact that it moves (a ship is not a stable place, either), I think he gets scared from the traffic noises and the sound of the car engine itself.
However, he has travelled with us in a car during numerous vacations (I never leave him back, no matter where I go) and 3 or 4 times he spent 7 to 9 hrs. in a car, without a problem. Of course in long trips, I pet him and hug him a lot, it makes him calm and happy. I also keep a bottle of water and pellets at hand, and he also travels in a small dog travel cage (a hard plastic one) filled with hay and a newspaper on the floor, which is changed during the travel whenever it gets wet or dirty.
Generally, if there is a choice (to travel by car or not) it's always best for the rabbit to avoid the travel, as, in some cases, rabbits have even gotten ill by excess travelling stress (if travelling during summertime heat stroke is another major danger).
Marietta