Invective from first person caught in traffic (6)
I believe the answer is:
tirade
'invective' is the definition.
(thesaurus)
'first person caught in traffic' is the wordplay.
'first person' becomes 'i'.
'caught in' is an insertion indicator.
'traffic' becomes 'trade' (I've seen this before).
'i' put into 'trade' is 'TIRADE'.
'from' is the link.
(Other definitions for tirade that I've seen before include "Long speech of angry criticism" , "strong words" , "Prolonged speech of abuse" , "Verbal onslaught" , "Broadside of denunciation" .)