Transport runs on iron railway (5)
I believe the answer is:
ferry
'transport' is the definition.
(I know that ferry is a type of transport)
'runs on iron railway' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'on' means one lot of letters go next to another.
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'railway' becomes 'ry' (abbreviation for railway).
'r' after 'fe' is 'fer'.
'fer'+'ry'='FERRY'
(Other definitions for ferry that I've seen before include "Boat for transferring people across short stretches of water" , "Ship for crossings" , "Boat across river" , "Transport across river etc" , "Bryan --, singer with Roxy Music" .)