In the car, on the train - IN and ON for vehicles

We are in the car but on the train, in the van but on the bus. Besides memorizing, is there any other way of knowing which to use?
You do not find one rules which works 100% but there are some guidelines which can be helpful:

1. If it is relatively small, smaller than a human body, then it does not have a compartment, so you cannot be inside it and you normally use "on": on a skateboard, on roller skates. Also, you are "on" things you sit on: on a bike (bicycle), on a motorbike (motorcycle), and of course on a horse.

2. If you sit inside and don't really have the ability to move around much, then you are "in" it: in a car, in a cab (taxi), in a van, in a single seat airplane.

3. If you can move about, the vehicle is relatively big, then you are "on" it: on a bus, on a train, on a boat, on a ship.

If we decide to take one of these, we get in or into the second group: get in the car, the taxi, the canoe. Later we get out of them.
On the other hand, you have to get on/onto and get off the ship, the plane, the bike.