It is not unusual for dogs to have behavior problems related to the car. Usually it is car sickness, fear of riding in the car and unruly or hyperactive territorial behavior. If your dog is either fearful of car rides or gets car sick, then you must show your dog that there is nothing to be afraid of and no reason to be sick. Many dogs associate car rides with something unpleasant or with previously being car sick. Reintroduce the car to the dog again slowly and in a non-stressful way.
Start out by just sitting in the car with the dog. Don't go anywhere. Don't even start the motor. Just sit in there and read a book or listen to the radio. Soon the dog will realize that nothing terrible has happened and that it did not get sick. Keep doing this until the dog is obviously relaxed and not fearful. If the dog does get sick, then you've stayed too long and should begin for shorter periods. When you see that your dog is comfortable with this activity, progress a little further and start the engine, but still do not go anywhere. When the dog is relaxed with the motor running, then begin taking very short trips, perhaps just around the block.
As your dog gets more and more comfortable, go for longer rides. Drive to places where the dog has fun. Take a short ride up the block to the dog's favorite walking area or to the beach, park or a friend's house. Let the dog associate car rides with fun, pleasant and rewarding experiences. Do not rush the dog into anything, or it may just slow down the process even further.
Some dogs associate the car with good times to the point of becoming overly excited. In this case, begin taking the dog for short rides that do not end up at the park or beach, but back home again. Teach your dog some obedience commands like down-stay. Sit in the car with your dog and practice there. Start out on a quiet street. Obviously do this with the car parked. You cannot drive and train the dog at the same time. Once the dog has mastered the down stay, then begin practicing in more distracting places. Make sure your dog can and will obey before giving the command in rush-hour traffic.
Alternatively, you can teach your dog to be calm in the car by restricting his movement via a crate or safety harness.
If the dog goes bonkers, barking, leaping and bouncing around in the car, just ask him to quiet and down-stay until the distraction passes or you arrive at your destination. There is no reason a dog shouldn't have good car manners. It is probably that you just haven't taught the dog what down-stay means in the car. Even a dog that knows these commands in the house or obedience ring will have trouble performing in the car until they practice there.