Commercial vehicle traffic (5)
I believe the answer is:
truck
This clue is a double definition.
'commercial vehicle' is the first definition.
(I've seen this in another clue)
'traffic' is the second definition.
(truck traffic is a kind of traffic)
(Other definitions for truck that I've seen before include "Lorry - wagon" , "Bargain" , "Vehicle (with which one has no dealings?)" , "commercial vehicle" , "Exchange" .)