Excludes barriers (4)
I believe the answer is:
bars
I believe this clue is a double definition.
'excludes' is the first definition.
('bar' can be a synonym of 'exclude')
'barriers' is the second definition.
(bar is a kind of barrier)
(Other definitions for bars that I've seen before include "Watering holes - units in musical scores" , "Establishments where alcoholic drinks are served" , "Prohibits; pubs" , "Obstacles" , "Metal rods or pubs" .)