As Steve rightly states you have choices, changing the settings in the CFG file, the automated navigation facility in some of the supermods or SH3 Commander.
In the early days following the map editing and inclusion of the canal I would spend 5 minutes plotting my course prior to engaging the engines and never wxperienced a problem, apart from that pier at the south west end on occasion
Alternatively you can go into the scripted campaign layer and delete the traffic in the area....but that wouldn't be my choice.