With hind-sight, perhaps, something reflective would have been helpful to driver (4-4,6)
I believe the answer is:
rear-view mirror
'with' is the definition.
I know nothing about this answer so I can't tell whether this works.
'hind-sight perhaps something reflective would have been helpful to driver' is the wordplay.
I cannot quite see how this works, but
'hind' could be 'rear' (synonyms) and 'rear' is found within the answer.
'sight' could be 'view' (synonyms) and 'view' is found within the answer.
The remaining letters 'mirror' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rear-view mirror that I've seen before include "Driver's aid" , "Driver glances at this" .)