Rail most of all, being stuck in vehicle traffic (10)
I believe the answer is:
balustrade
'rail' is the definition.
(balustrade is a kind of rail)
'most of all being stuck in vehicle traffic' is the wordplay.
'most of' means to remove the last letter.
'being stuck in' is an insertion indicator.
'vehicle' becomes 'bus' (public transport vehicle).
'traffic' becomes 'trade' (traffic can mean illegal trade).
'all' with its last letter taken away is 'al'.
'al' inserted into 'bus' is 'balus'.
'balus'+'trade'='BALUSTRADE'
(Other definitions for balustrade that I've seen before include "feature of terrace, perhaps" , "Form of railing" , "Handrail" , "Railing on stairs or balcony" , "Parapet" .)