Illegal trading of vehicles on a highway? (7)
I believe the answer is:
traffic
This clue could be a double definition.
'illegal trading' is the first definition.
(I've seen this before)
'vehicles on a highway?' is the second definition.
'traffic' can be an answer for 'vehicles' (I've seen this before). I am unsure of the 'on a highway?' bit.
'of' is the link.
Can you help me to learn more?
(Other definitions for traffic that I've seen before include "Passing vehicles - trade" , "Movement of vehicles" , "Illegally push" , "Illegal trading" , "Deal illegally in vehicles?" .)