Crossword Genius

Container causing a traffic problem and a shock (3,3)

Ross

I believe the answer is:

jam jar

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

'container causing a traffic' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'problem and a shock' is the wordplay.
'problem' becomes 'jam' (I've seen this before).
'and' means one lot of letters go next to another.
'a shock' becomes 'jar' (I've seen this before).
'jam'+'jar'='JAM JAR'

Can you help me to learn more?

(Other definitions for jam jar that I've seen before include "Container for conserve" , "Container for preserve" .)

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