Parking, about to deliver lead (7)
I believe the answer is:
precede
'lead' is the definition.
(synonyms)
'parking about to deliver' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'about' becomes 're' (regarding).
'to deliver' becomes 'cede' ('cede' can be a synonym of 'deliver').
'p'+'re'+'cede'='PRECEDE'
(Other definitions for precede that I've seen before include "Come or go before" , "Go ahead of" , "go before the others" , "Go before (someone)" , "Having to come in front" .)