Trade vehicles (7)
I believe the answer is:
traffic
This clue is a double definition.
'trade' is the first definition.
(I know that traffic is a kind of the trade)
'vehicles' is the second definition.
(I've seen this before)
(Other definitions for traffic that I've seen before include "Vehicles on the road" , "Illegal trading" , "Business" , "Truck" , "Vehicle flow" .)