why people vomit in bus journey or while traveling ?

this was the question came to my mind when i saw a person on other bus puked( vomiting) through window, recently i been to my friends marriage in chittoor(a small town in south india) though this is the second time bus journey in my life for such a long distance i never felt like puking in the bus in the whole trip this time, funnily i heard a little conversation of mother and child about this subject in back seat, child: "mom why that person is vomiting" : Mother: "because that person does not like the smell of diesel" was that answer rite? pretty good for a child of 4 years! though vomiting in the bus terminals is common sightings every where... so what is the real reason behind this puking thing?

After googling for a while i came across many factors why people vomit during journey but three was most common in many cases the points are in the relevancy.

1. 80% of the time vomitting happens due to simple factor called "Motion Sickness" also called travel sickness is a condition in which a disagreement exists between visually perceived movement and the vestibular system's sense of movement. because of this body fails to adapt the changes in equilibrium due to which people vomit and this mostly happens to people while traveling in Ghat section where the route is curvy and steep.

2. Other reason is in rare cases people might have allergies to smoke, change in environment, or reflux to diesel fumes this may tends to cause nausea or vomitting sensation.

3. And in few scenarios eating lot of junk and oily foods during journey may contribute to this factor.

and between i also puked once in my first bus journey while traveling in the ghats of kerala while going to munnar and weirdly almost 50% of the people in the bus vomited from small kids to elderly persons, so have you guys ever puked then leave your experience.