Byers' sell-out affected current transport (12)
I believe the answer is:
Here is my best explanation:
'current transport' is the definition.
'byers' sell-out affected' is the wordplay.
'affected' indicates an anagram.
'byerssellout' is an anagram of 'TROLLEYBUSES'.
(Another definition for trolleybuses that I've seen is "Vehicles".)