HI
Would you say that both of the following sentences are correct and natural?
Many thanks,
Tom
Hi Tom
“On the bus” is a commonly used collocation, of course. However, I’d say you could use either one. What’s the broader context? I’d say the use of “in” will focus the idea more exclusively and literally on the idea of “inside” (rather than “outside”).
.
Hi, Amy
So, if somebody from work calls me on my cell phone to inquire where I am (suppose I’m running late), I can reply:
I’m on the bus/trolleybus/tram right now, in two minutes will be at work
Thanks !
Hi Alex
Yes, I’d use “on” to indicate that I am currently a passenger on a bus/train/trolley.
.
Thank you, Amy
In fact, it is a very frequently used phrase, seeing as (at least in my country) people often call each other on cellular phones only to ask where they are at the moment. 
(like “where are you?” “I’m on the bus”)
Not only in your country, believe me. This is what you’d here any given day of the week (of course, you don’t usually hear the person on the other end):
‘Hel-lo!’
…
‘Hey Jimmy, how’s tricks.’
…
‘I’m on the 15B into town, ya know, still on Rathgar Road stuck in bleedin’ traffic just before the roundabout in Rathmines, ya know, probably another 5 to 10 minutes to Swan Centre I’d say, so it’d be like 5ish till I get to Dame Street, right, but I’ll sure meet ya some time between half 5 and 6 at the Burger King on Grafton, I reckon.’
…
‘Oh, yer not coming out tonight. Fair play to you, not a worry, talk to ya soon.’
.
On the off chance that you’re all misinterpreting my first post, the expression “on the bus” is definitely the most likely collocation you’ll hear. It’s very commonly used.
However, a possible use of “in” cannot be completely ruled out. The broader context could actually make “in” more appropriate.
.
Hi Amy,
Could you please be more specific about the broader context?
Many thanks,
Nessie
Yes. “One the bus” normally has the meaning of “I’m traveling”.
Hi Molly,
I think you’ve hit the nail on the head - on the bus = travelling by bus. In the/a bus = location inside the bus.
Alan
Indeed. And what about “I’m in/on the toilet”? :oops: 
In this context:
in the = location
on the = location and action
Hi Nessie
Using “on the bus” includes the general idea of “in” but also focuses on the idea of the bus as a means of transportation. Depending on the broader context, you might want to focus exclusively on the idea of physically being inside the bus (in contrast to being outside the bus). Something like this, perhaps:
We had broken down, and while we were waiting in the breakdown lane for road service, a tractor-trailer nearly sideswiped our bus. The truck hit six of the people who’d left the bus. All six of them died. Fortunately, I was in the bus when the accident took place, and that probably saved my life. If I’d been standing next to the bus like those other six people, that truck might have killed me too!
.
Which of the following is correct?
i) I’m sitting on the bus.
ii) I’m sitting in the bus.
People usually say “on the bus.” Actually, I’ve never heard anybody say “in the bus.” I never thought about this before, but I guess it’s pretty odd.
So, is it correct to say ‘I’m sitting on the car’?
Unless you’re on top of it, no, it is not. lol
So it should be ‘I’m sitting on the bus’ and ‘I’m sitting in the car’?
That is how it usually goes.
Hi Leong187,
You can commit to memory. It’s quite easy.
on a bus, on a train, on a plane, on a ship but in a car/ in a taxi.
Hi Leong,
The difference between ‘on’ and ‘in’ for transport has mainly to do with size. In other words large vehicles such as buses, trains, planes, ships are usually ‘on’. Smaller methods of transport such as a car are usually ‘in’.
Alan