> Say 0.2% on aggregate, that's 5% for the whole journey, 10% because the ship is empty half the time.

Fuel saves from slow steaming and being empty are massive.

> If this were true, even neglecting oil burnt for heating or electricity or aviation, you'd expect 40% of the vehicles to be tanker trucks.

The US has a lot of domestic pipelines [1], and a lot of the remainder is done by train [2] because trains are the most efficient way to transport bulk goods over extremely long distances.

[1] https://www.bts.gov/geography/geospatial-portal/us-petroleum...

[2] https://www.aar.org/wp-content/uploads/2018/07/AAR-US-Rail-C...