Although we often think of dogs as happily lolling out the car window enjoying new scents, all pets are not alike. A car ride can equal an anxiety attack and shaking, drooling, and even vomiting for some dogs. And while some cats hide under the car seat, we know of one kitty who was perfectly content to lay on the dashboard and watch the world go by!
Although your pet may exhibit symptoms such as drooling or vomiting, this is not usually what humans experience as car or motion sickness, which is an inner ear problem. Although some pets can have inner ear motion sickness, your pet's fear of driving is probably caused by a combination of fear and lack of environmental control. To your pet, the car feels like a very noisy moving place that inundates him with all sorts of odors. He does not understand that he will be safe and sound somewhere after the car ride.
With this type of systematic progression, your pet should be used to driving by the time you get ready to leave on your longer trip. If your dog simply will not get settled, consider using Drs. Foster & Smith Ultra-Calm® or another pet-calming product like Comfort Zone® Spray or Rescue Remedy, all non-prescription products that will ease your pet's anxiety.