The prepositions of transport (on - in - by) allow you to discuss the way you travel or have travelled from one place to another. In general we use 'on' for public transport, 'in' for private transport and 'by' to explain a type of transport, transportation environment or the surface area.
ON - transportation on which you can move
“I can’t call right now, I’m on the bus”.
“We were served a declious meal on the ferry”.
“Let me give you a ride – hop on the back of my bike”.
We use on when you can stand, walk or sit on top of the vehicle. Most commonly we use on for public transport; transportation on which you can move even though the vehicle itself is in motion. In this case you can approach ‘on’ as a synonym of ‘inside’
E.g. planes, trams, ferries, subways, trains, ships, bikes, skatesboards, skis, motorcycles, etc.
IN - private transport
“”I can seat only 3 people in my car”.
“The driver doesn’t allow dogs in his taxi”.
“We hardly had any space to move in the helicopter”.
We use in when we are inside the vehicle and do not have much room to move. Most commonly in is used for private transport – when you don’t share the vehicle with (unknown or) other passengers.
E.g. cars, taxis, trucks, vans, etc
- Note: we can use in with public transport, when we emphasise the space of the type of transport, not the journey – e.g. “It was very humid in the plane”
BY - ways and modes to travel
“I go to work by tram, every morning”.
“To see more of the surroundings, we prefer to travel by sea”.
“We got there by boat, but returned by plane”.
We use ‘by’ to describe the mode (or way) of travel. By is used either after a verb or a noun.
E.g. journey, voyage, car, bus, plane, road, sea, air etc.
BY - ON foot - the same rules applies
Generally you will hear and see ‘on foot’ is more common – you are literally on top of your feet moving from one place to another. However, ‘by foot’ equally makes sense, as you describe your way of travelling.