A parking toll leading to petition (6)
I believe the answer is:
appeal
'to petition' is the definition.
(appeal is a kind of petition)
'a parking toll leading' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'toll' becomes 'peal' (synonyms).
'leading' says to put letters next to each other.
'a'+'p'+'peal'='APPEAL'
(Other definitions for appeal that I've seen before include "Earnest or urgent equest" , "Draw" , "Attraction, pleasantness" , "Petition or attraction" , "Supplication to take a higher court" .)