All suggestions I've read so far are great. But I'd like to add one for you that I didn't see. Try bring treats into the car with you. When the dog gets inside - give a treat. When the dog sits quietly - give a treat. When you start the engine - give a treat. If the dog starts to associate good things with being in the car, it may become less anxious. I wish I had this forum for help when I had my poodle. He hated car rides as much as your dog does! I've learned so much since then, but he's in doggy heaven now, so car rides aren't a problem for him anymore, and luckily my new puppy loves them!
Give it a try at least - it can't hurt! Good Luck!