Have to do with traffic (4)
I believe the answer is:
deal
'traffic' is the definition.
(I've seen this in another clue)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for deal that I've seen before include "understanding" , "Transact" , "Bargain or kind of wood" , "Fir or pine wood" , "Large quantity (of wood?)" .)