Outburst from one caught in traffic (6)
I believe the answer is:
tirade
'outburst' is the definition.
(thesaurus)
'one caught in traffic' is the wordplay.
'one' becomes 'i' (Roman numeral).
'caught in' indicates putting letters inside.
'traffic' becomes 'trade' (I've seen this before).
'i' inserted inside 'trade' is 'TIRADE'.
'from' acts as a link.
(Other definitions for tirade that I've seen before include "Fulmination" , "Verbal outburst" , "Vocal abuse" , "Long angry harangue" , "A tongue-lashing" .)