Final answer:
The world's heaviest shipping routes are influenced by commercial trade and ship type. Bulk carriers have changing routes based on market demands, while container ships follow regular routes with frequent stops.
Step-by-step explanation:
The world's heaviest shipping routes are determined by the nature of commercial trade and the type of ship being used. Bulk carriers, which carry large quantities of dry goods like ores, grain, and coal, typically transit between two ports either fully loaded or in ballast. These routes can change frequently based on market demands. Container ships, on the other hand, tend to follow more regular routes with frequent stops along the way.