Our LD used to get terribly sick in the car, it got so bad he wouldn't even get in the car - we had to lift him in and at 70lb that wasn't much fun!! Our vet told us to use Gravol (Dramamine) and it did work. We got the infant liquid formula and I used a syringe to squirt it down his throat. We only used it a few times (maybe four) to get him over the worst of it and then didn't need to anymore. I think once they have had a couple of journeys without feeling sick, they get over it pretty quickly.
I have the same problem. I think it is overexcitment for Max. I harnessed him into the rear seat but, he always would vomit when the car stopped going TO somewhere. He is always fine on the way back home. Then we started sitting in the back with him or put him in the front seat harnessed and he improved. Now, again, he is getting car sick even when next to us and the window open. I'm praying he outgrows it but, I must admit, I don't feel too confident.