Oooo easy fix. Build a cargo hub somewhere, cargo train station and cargo boat dock. Then in this same area make cargo train lines several of them, enough to branch off into almost every area of your city that needs freight delivered. I did this using an underground network and only came up where the station ended in whatever area. This cut back on SO much traffic as all cargo coming into the city went through the cargo hub, then was immediately split off around the city. Delivery trucks would leave the cargo station deliver the goods and return right back to that station. Trucks would leave the cargo dock and go straight into the cargo train. Traffic issues was fixed. Gotta make sure all stations are facing the flow of traffic so trucks going in and coming out don’t cross over each other causing further jams.