A great story that qualifies these days as urban myth... but there is also a short story written by E F Benson, called 'The Bus Conductor' (e-text at
http://www.horrormasters.com/Text/a0209.pdf) which is essentially the same thing. E F Benson wrote his version in 1906.
I wonder if the story existed before Benson's version? I think it's quite likely. Does anybody know?