Pointless proposal messes up maps of motorway exits (3,5)

I believe the answer is:

off ramps

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

'pointless proposal messes up' is the definition.
I know nothing about this answer so I can't judge whether this works.

'maps of motorway exits' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'maps' is 'amps' which is within the answer.
'of' could be 'o' and 'o' is located in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

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

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