Crossword Genius

Most occupied vehicle that's by street (7)

Ross

I believe the answer is:

busiest

'most occupied' is the definition.
('busy' can be similar in meaning to 'occupied')

'vehicle that's by street' is the wordplay.
'vehicle' becomes 'bus' (I've seen this before).
'that's' becomes 'ie'.
'by' says to put letters next to each other.
'street' becomes 'st'.
'bus'+'ie'+'st'='BUSIEST'

(Another definition for busiest that I've seen is " Most active or crowded".)

I've seen this clue in The Guardian.
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