Hi there... Its something he has to grow out of. Meka is 1 yr and shes and she's still growing out of it. She's much better than she was as a baby, but still working on it... The best thing to do it to keep taking him for rides so that he can get better
But, I do advise you not to allow him to eat/drink before taking a long car rides. Because they are so nervous, the eating will only cause them to vomit or poop and makes for a messy car ride...