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Crossings on grand overpasses going up and down, we hear (8)

Ross

I believe the answer is:

singsong

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'overpasses going up and down we hear' is the definition.
I can't judge whether this defines the answer.

'crossings on grand' is the wordplay.
'crossings' becomes 'sings' (I can't justify this - if you can you should give a lot more credence to this answer).
'grand' becomes 'g' (synonyms).
'sings'+'on'+'g'='SINGSONG'

Can you help me to learn more?

(Other definitions for singsong that I've seen before include "monotonous rhythm" , "Informal musical gathering" , "Informal community music-making" , "Friendly musical session" , "With a rise and fall of voice in speaking" .)

I've seen this clue in The Independent.
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