Garda in mess after motorway becomes town's high street (4,4)

I believe the answer is:
main drag
'street' is the definition.
(I know that main drag is a type of high street)
'garda in mess after motorway' is the wordplay.
'mess' indicates an anagram.
'after' means one lot of letters go next to another.
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'garda'+'in'='gardain'
'gardain' with letters rearranged gives 'aindrag'.
'aindrag' after 'm' is 'MAIN DRAG'.
'becomes town's high' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
I've seen this clue in The Irish Times.
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