I have had same problem today. My 6 month old can manage an hours journey but then she becomes sick. I am going to speak to the vet and see if they can prescribe something to help her
Age? Jax used to always get sick in the car and there would always be vomiting. Couple things to try, make sure he has an empty stomach, Benadryl, ride in a car seat up high. Jax finally grew out of it (I think) but he is 11 now.