Vomiting can occur for many reasons, especially when traveling in vehicles, especially buses and planes. Such as excessive shaking , many people vomit for AC , etc. But many people vomit without any reason. Basically it is for nervous weakness. For those whose nerves are weak , the brain cannot accept the movement of the house with the house closed while traveling. The brain sees that the legs are not moving but the nerves are signaling to walk and behave again and the eyes are still fixed inside the car. In this condition the brain assumes that there is some poison in the stomach so it is happening. As a result, the brain vomits and tries in vain to get rid of the poison. Now the question is how to strengthen the nerves. For this you need to eat food with vitamin D (egg white part). You have to see the outside view while traveling.