Transport official parking in trendy part of town (9)
I believe the answer is:
inspector
'transport official' is the definition.
(ticket inspector)
'parking in trendy part of town' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'in' is an insertion indicator.
'trendy' becomes 'in' ('in' can mean fashionable).
'part of town' becomes 'sector' (sector can mean an area).
'in'+'sector'='insector'
'p' put inside 'insector' is 'INSPECTOR'.
(Other definitions for inspector that I've seen before include "Examining official" , "Person whose job it is to examine efficiency as in schools" , "leading rank" , "controller" , "bluebottle!" .)