Passes across; first try moved very fast, then takes a seat (8)

I believe the answer is:

transits

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'passes across' is the definition.
('transit' can be a synonym of 'pass across')

'first try moved very fast then takes a seat' is the wordplay.
'first try' becomes 't' (rst letter of 'try').
'moved very fast then' becomes 'ran' (I can't justify this - if you can you should give a lot more credence to this answer).
'takes a seat' becomes 'sits' (I've seen this before).
't'+'ran'+'sits'='TRANSITS'

Can you help me to learn more?

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

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