Takes advantage of public transport (not second-class) (4)
I believe the answer is:
uses
'takes advantage' is the definition.
(I've seen this in other clues)
'public transport not second-class' is the wordplay.
'public transport' becomes 'buses' (I've seen this before).
'not' indicates named letters should be taken away.
'second class' becomes 'b'.
'buses' with 'b' removed is 'USES'.
'of' is the link.
(Other definitions for uses that I've seen before include "Employments" , "Sues (anag.)" , "Functions, applications" , "'Purposes, functions (4)'" , "Utilises" .)