Engineer ran good railroad (7)
I believe the answer is:
dragoon
'railroad' is the definition.
('dragoon' can be a synonym of 'railroad')
'engineer ran good' is the wordplay.
'engineer' indicates anagramming the letters.
'ran'+'good'='rangood'
'rangood' with letters rearranged gives 'DRAGOON'.
(Other definitions for dragoon that I've seen before include "Harass" , "Shanghai" , "Press" , "[CARIBINEER]?" , "Old heavy cavalryman" .)