I entirely agree with donay.
According to my copy of The Ins and Outs of Prepositions
indicates travel in vehicles
in which one can walk.
We can see John and Mary on the bus meaning, you actually see both of them probably standing, moving or seated inside by the window of a moving (or idling) bus.
Typical nouns you use on
with: airplane, bus, ship, train, spaceship, UFO.
Typical verbs you on
before: get, go, ride, sit, travel.