Driving Tank Vehicles Safely: Rollover Risk, Center of Gravity, and Load Effects
What this domain tests
This section covers driving tank vehicles safely, with emphasis on rollover risk, center of gravity, and load effects. The exam tests rollover physics: tank vehicles carry liquid mass high above the road, and the center of gravity changes with load.
Core rules
- A loaded tank usually has a higher center of gravity than an empty one, so it rolls over at lower lateral acceleration.
- High-density liquids such as acids, caustic solutions, and heavy oils add more weight for the same volume; check axle and gross weights.
- A full tank has little free surface and less surge, but its mass is still high; a partially full tank can combine a high center of gravity with severe surge.
- Enter curves below the posted or advisory speed; do not brake hard once the vehicle is leaning.
- Keep the load centered and secured; an off-center or shifted load raises rollover risk.
Worked example
A tanker with a half-full load of heavy liquid approaches a 25 mph ramp curve posted for cars. The driver thinks the truck can take it at 25 because the tank is only half full. Reasoning: half-full means a free surface and surge; the heavy liquid also keeps the center of gravity high. The combination can produce a strong outward surge and a lean that the suspension cannot control. The safe action is to slow well below 25 before the curve, use a smooth steering input, and avoid braking in the curve.
Traps
- Believing a full tank is always the most dangerous; surge is lower when full, though the center of gravity is high.
- Using the car posted speed as a truck target.
- Braking hard in a curve to correct a fast entry.
- Ignoring weight limits because the tank is not visibly full.