An incentive to private transport? Nonsense! (6)
I believe the answer is:
carrot
'an incentive' is the definition.
(thesaurus)
'private transport? nonsense' is the wordplay.
'private transport?' becomes 'car' (I've seen this before).
'nonsense' becomes 'rot' (I've seen this before).
'car'+'rot'='CARROT'
'to' is the link.
(Other definitions for carrot that I've seen before include "Red vegetable used as inducement" , "Vegetable - incentive" , "Tapering vegetable" , "Rewarding vegetable?" , "The vegetable for persuasion" .)