Transport a road vehicle by railway (5)
I believe the answer is:
carry
'transport' is the definition.
(I know that transport can be written as carry)
'a road vehicle by railway' is the wordplay.
'a road vehicle' becomes 'car' (vehicle driven on the road).
'by' means one lot of letters go next to another.
'railway' becomes 'ry' (abbreviation for railway).
'car'+'ry'='CARRY'
(Other definitions for carry that I've seen before include "Be pregnant (with)" , "(Of sound) be audible at a distance" , "Move" , "range" , "Bear, tote" .)