Crossword Genius

Sell preserves when roads are gridlocked (7,3)

Ross

I believe the answer is:

traffic jam

I'm a little stuck... Click here to teach me more about this clue!

'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" .)

I've seen this clue in the Sydney Morning Herald.
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