Is sleeping the only way to avoid vomit in long land journey?

I sometimes will go to mountainous area for vacation and the problem is that I will vomit at least once for every journey (other people will also vomit in the car), and sleeping pills are my only friends for this situation.

I’ve tried not to read, not see the scenery, open the window, eat solid/sweet/sour food, etc but it just won’t work. Extremely long journey with car and spinning roads with different elevation are the cause of all these troubles!