Commuter option (4)
I believe the answer is:
rail
'commuter option' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rail that I've seen before include "Bar of rolled steel" , "Waterside bird; part of track" , "Complain intemperately" , "Bar of track or fence" , "Bar - marsh bird" .)