British and American transport (3)
I believe the answer is:
bus
'transport' is the definition.
(busing is a kind of transporting)
'british and american' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'and' is a charade indicator (letters next to each other).
'american' becomes 'US' (abbreviation for United States).
'b'+'us'='BUS'
(Other definitions for bus that I've seen before include "People carrier" , "eg Double-decker" , "Coach" , "Road vehicle able to carry many passengers" , "Large passenger vehicle - small business!" .)