Rail route used by Berliners (4)

I believe the answer is:

line

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'rail route' is the definition.
'line' can be an answer for 'route' (line is a kind of route). I am not certain of the 'rail' bit.

'used by berliners' is the wordplay.
'used by' says the answer is hidden in the clue.
'LINE' is hidden in the letters of 'berliners'.

Can you help me to learn more?

(Other definitions for line that I've seen before include "Fill" , "Row - occupation" , "Wrinkle; phone link" , "Long mark; direction" , "A length without breadth or thickness" .)

I've seen this clue in the Evening Standard.

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