Maintained parking's booked (9)
I believe the answer is:
preserved
'maintained' is the definition.
(similar in meaning)
'parking's booked' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'booked' becomes 'reserved' (similar in meaning).
'p'+'reserved'='PRESERVED'
(Other definitions for preserved that I've seen before include "Prevented from decaying or spoiling" , "Kept in an unaltered condition" , "Kept safe from harm" , "Prevented from decay" , "Maintained in an unaltered condition" .)