Basic answer: We say "on" for transport that you have walking space to move around in. On a bus On a train On a plane On a cruise We say "in" for things that you just get into with minimal space to walk around. In a car In a (paddle) boat In a helicopter

to expand upon Ellis's answer which is correct and a simple way to remember. in the UK we say "on" for public transport that is shared with many others. and we say "in" for transport that is for our selves only (or small group) and private. taxis. a car etc. It comes from going aboard a ship. the first form of public transport, then when trains, planes and other things were invented the usage spread to these forms of transport.

to get in/to get on: to enter or to board a vehicle To get in is used for cars, to get on is used for all other forms of transportation. - It's easiest to get in the car from the driver's side. The door on the other side doesn't work well. - I always get on the bus to work at 34th Street. to get out of/to get off : to leave or to descend from a vehicle To get out of is used for cars, to get of is used for all other forms of transportation. - Why don't we stop and get out of the car for a while? - Helen got off the train at the 42nd Street terminal. For practice and understanding of in/on/at try "Essential Grammar in Use" by Murphy. There are 2 units dedicated to it there.