Transport artist in box (5)
I believe the answer is:
train
'transport' is the definition.
(train is a kind of transport)
'artist in box' is the wordplay.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'in' means one lot of letters goes inside another.
'box' becomes 'tin' (I've seen this in other clues).
'ra' inserted into 'tin' is 'TRAIN'.
(Other definitions for train that I've seen before include "Teach, retinue" , "Engine and carriages" , "Exercise in preparation for some event" , "Railway service" , "Rail transport" .)