RE: "How come you didnt use the same math for the bandwidth of the train ? Say the train carries 800 people, 80 kmph and the train length is 100m. Then you get a bandwidth of 177 per second. "

CORRECT

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RE: "And even logically a train moving 800 people at once at 80kmph, and a bus moving 60 people at 5kmph should have a lower bandwidth than the train. Confused !"

You are comparing one bus to one train. I'm comparing a system of busses to a system of trains. That's the difference.

The maximum bandwidth of a single train is much more than that of a system of trains.