In transit, seeing red caviar boxes a dull experience (4,4)
I believe the answer is:
road rage
'in transit seeing red' is the definition.
(getting angry when travelling in a car)
'caviar boxes a dull experience' is the wordplay.
'caviar' becomes 'roe' (fish eggs).
'boxes' indicates putting letters inside (the outside letters must 'box' inside letters in).
'dull experience' becomes 'drag' (if something's a drag it's very boring).
'a'+'drag'='adrag'
'roe' enclosing 'adrag' is 'ROAD RAGE'.
(Other definitions for road rage that I've seen before include "traffic hazard" , "making of a scene for travellers?" , "Violently aggressive behaviour by driver" , "Uncontrollable temper experienced by some drivers" , "Driver's fury" .)