Whether travelling by car or plane, it is of the utmost importance that your carrier be properly tagged and labelled. Even if the carrier will be in the back seat of your car at all times, you must label it thoroughly in case of an accident. The general consensus is, no, it is not necessary to sedate or tranquilize your cat and can be downright dangerous if the cat will be traveling by air. When travelling by car, your cat should be confined to a carrier at all times. It is wise to always secure the carrier with a seat belt.
Loose carriers can be dangerous projectiles in an accident situation.
The majority of cats will curl up and sleep after a period of meowing just to let you know that they are there. If their favorite cat bed is in the carrier, they will most likely be much happier. If your cat does have a known aversion to travel in a car and you must take him along, you can choose to discuss the use of sedatives with your veterinarian. Always carry bottled water with you and bring along your cat's favorite food, just in case you get stranded or need to stop along the way. You will also want to have a litter pan and litter in the car in case it is needed.