Below you will find a desensitization program that may help with the carsickness issue:
If your dog has a history of getting carsick when you travel, make sure he doesn’t eat for 6-12 hours prior to your travel time.
Place your dog in the car while it is still in the driveway, making sure he has his favorite toy with him. Stay in the car for a couple of minutes, and then leave him alone for a short period of time. Do this a few times a week until you reach the point where he is not getting sick. Increase the amount of time in the car each day, assuming sickness is not an issue.
Repeat the process as outlined above, only this time leave the car engine running. Again, increase the amount of time he spends in the car if he is not getting sick.
With the car idling in the driveway, place the dog in the vehicle and start driving backwards and forwards. This is usually best done with two people: one driver, one dog handler. Perform this practice a few times a week until he starts to get comfortable, and then make the move to the next level.
Take the car out of the driveway and go around the block ONCE. Do not push it right away. When you see he is comfortable after a few days, move it up to two blocks.
NOTE: Never move on to the next step until all visible signs of carsickness have been removed. If you have to do shorter exercises over long periods of time, then so be it. Your goal is to make your dog feel comfortable and reach a point where carsickness is no longer an issue.
Take a drive to a local convenience store or some other nearby place, and then leave him in the car for a few minutes. If you have a dog that panics when left alone, bring along a handler.
You can see how each incremental step will get you one step closer to curing the carsickness problem. Be prepared to do this for anywhere from a week to a couple of months.