Transportation a bighead uses (5)

I believe the answer is:

buses

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'transportation a' is the definition.
I can't tell whether this defines the answer.

'bighead uses' is the wordplay.
'bighead' becomes 'b' (head letter of 'big').
'b'+'uses'='BUSES'

Can you help me to learn more?

(Other definitions for buses that I've seen before include "Passenger vehicles" , "Public transport vehicles" , "Public service vehicles" .)

I've seen this clue in the Evening Standard.

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