Driving Tank Vehicles: Surge, Slack Load, and Load Shift Control
Tanker driving is about controlling a moving free surface. The Tanker Test tests whether you understand surge, slack loads, and load shift, and whether you can apply smooth-control techniques before the liquid moves the truck.
What the load is doing
A partly filled tank has a free surface. When you accelerate, liquid surges rearward; when you brake, it surges forward; when you turn, it shifts side to side. A slack load is cargo with space to move, so it is not held tight against the tank ends or baffles. Baffles divide the tank and reduce surge, but they do not eliminate it. A smooth-bore tank is worse, and a partially filled tank is usually more dangerous than a full or empty one because the liquid has room to build momentum.
Control techniques
Start gently and accelerate smoothly. Shift up without jerking. Brake early and gently, and leave a longer following distance than a light vehicle needs. Slow down before a curve, then hold a steady speed through it; do not stab the brakes in the curve. Before a downgrade, select a low enough gear and use engine braking as appropriate, but avoid abrupt throttle or brake changes. Keep compartments loaded within limits and distribute weight so the tank is not badly unbalanced.
Worked example
A tanker with a partial load approaches a downhill stop sign. The driver brakes late, feels the liquid push forward, and brakes harder. The reasoning: the first hard brake starts the surge, and the second makes it worse. The better approach is to slow early, select a lower gear, brake progressively, and stop with room ahead so the surge does not force a panic stop.
Traps that cost marks
Believing baffles make a tank safe; thinking a full tank cannot surge; using the posted curve speed as a tanker speed; and making sudden lane changes. The test wants smooth inputs and space, not aggressive correction.