Sell preserves when roads are gridlocked (7,3)
I believe the answer is:
traffic jam
'roads are gridlocked' is the definition.
I can't tell whether this definition defines the answer.
'sell preserves' is the wordplay.
'sell' becomes 'traffic' (I can't explain this - if you can you should give a lot more credence to this answer).
'preserves' becomes 'jam' (jam is a kind of preserves).
'traffic'+'jam'='TRAFFIC JAM'
'when' is the link.
Can you help me to learn more?
(Other definitions for traffic jam that I've seen before include "could make driver late" , "Vehicular snarl-up" , "stuck in this" , "Gridlock" , "Problem, in a way" .)