Drive home, smashing gate on bridge (3,6)
I believe the answer is:
get across
'drive home' is the definition.
(both can mean to succeed in conveying something)
'smashing gate on bridge' is the wordplay.
'smashing' is an anagram indicator.
'on' says to put letters next to each other.
'bridge' becomes 'cross' (I've seen this in other clues).
'gate' is an anagram of 'geta'.
'geta'+'cross'='GET ACROSS'
(Other definitions for get across that I've seen before include "Manage to communicate" , "Communicate successfully" , "what crucifer must do first of all" , "Go over - explain" , "Express" .)