Barrier keeping tons off path (4)

I believe the answer is:

rail

'barrier' is the definition.
(rail is a kind of barrier)

I cannot understand how the remainder of the clue works.

(Other definitions for rail that I've seen before include "Abuse, scold" , "Complain vehemently" , "Fulminate - wading bird" , "Kind of transport" , "Scold, berate" .)

I've seen this clue in The Times.

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