Shade over broken post is hazard for driver (5,4)
I believe the answer is:
blind spot
'hazard for driver' is the definition.
(I've seen this before)
'shade over broken post' is the wordplay.
'shade' becomes 'blind' (I've seen this before).
'over' is a charade indicator (letters next to each other).
'broken' indicates anagramming the letters.
'post' is an anagram of 'spot'.
'blind'+'spot'='BLIND SPOT'
'is' is the link.
(Other definitions for blind spot that I've seen before include "Area where understanding is lacking or one is unsighted" , "Hazard for driver" , "source of misunderstanding?" , "where one cannot see" , "Area where vision is obstructed" .)