What is the primary danger when driving an articulated fuel tanker that is only 50% to 70% full (partially loaded)?

1. Severe liquid surge occurs inside the tank, shifting thousands of kilograms of mass forward during braking and outward during turns, easily flipping the truck
2. A partial load is lighter, so the tanker is inherently more stable than when full
3. The vapour space above the liquid cushions the load and damps out movement
4. Baffles inside every tanker prevent the liquid from moving at all