Transport by automobile and railway (5)
I believe the answer is:
carry
'transport' is the definition.
(I know that transport can be written as carry)
'automobile and railway' is the wordplay.
'automobile' becomes 'car' (synonyms).
'and' is a charade indicator (letters next to each other).
'railway' becomes 'ry' (abbreviation for railway).
'car'+'ry'='CARRY'
'by' acts as a link.
(Other definitions for carry that I've seen before include "range" , "Stock" , "(Of sound) be audible at a distance" , "Transport; transmit" , "Be pregnant (with)" .)