Get in vs. get on [duplicate]

Memorization is probably the best approach for learners. Rules are not always helpful or learnable! That said, I actually think this is just the normal use of the two prepositions applied to vehicles. We use "in" when there's an enclosing space, so not for a bike, or horse, but for a car, van, or motorbike sidecar. However, this tends to be overridden if the vehicle is high off the ground (and so involves a bit of climbing), and in these cases, we prefer "on": plane, bus, etc. I think we can see this with truck: "in" sounds OK, but if it was a monster truck, "on" would seem more appropriate. And even with a normal truck, "in" would only be used for the cab; "on" would be prefered for the flatbed at the back.

I would say that, in general, on is used in two cases:

• When you mean atop (hence, get on a bicycle or a motorcycle)

• When it's used as a shortened form for on board (hence, get on the plane, get on the train)

Otherwise, you can use in for getting inside vehicles (hence, get in the taxi).

This explains why I'd be more inclined to tell my kids to get in the van (when referring to the family van parked in our driveway), but I might say that I need to get on the van (when referring to a shuttle van going to or from an airport or hotel).