How Long Have You Been on a Bus?

When do we use in and when do we use on in relation to modes of transport? For example, I'm in the car, but I'm on the bus. Is there a rule behind this, or at least a loose rule? So with public transportation, generally, we use on. It says like we have on the bus, on the train, on a ferry. On a plane? And you know, you're in a truck,. You're in a car. Yeah. Okay. Let's quickly wrap this up and let's move on to today's...