Check retrograde public transport's expected to arrive (6)
I believe the answer is:
subdue
'check' is the definition.
(subduing is a kind of checking)
'retrograde public transport's expected to arrive' is the wordplay.
'retrograde' shows that the letters should be reversed in order.
'public transport's' becomes 'bus'' (bus is a kind of public transport).
'expected to arrive' becomes 'due' (I've seen this in another clue).
'bus' back-to-front is 'sub'.
'sub'+'due'='SUBDUE'
(Other definitions for subdue that I've seen before include "Force to yield, tame" , "Overcome, force to yield" , "Bring under control, tame" , "Quash" , "'Quieten, bring under control (6)'" .)