Driving Tank Vehicles Safely: Rollover, Surge, and Braking
This domain tests why a tank behaves differently from a van: the load is liquid, the center of gravity is high, and the product moves. Most tanker crashes in the exam scenarios are rollovers and loss-of-control stops.
Surge and outage
- Outage is the empty space above the liquid. More outage means more room for the product to shift.
- Smooth-bore tanks let liquid run the full length: it surges rearward when you accelerate, forward when you brake, and side to side in curves and lane changes.
- Baffles divide the tank and reduce - but never eliminate - front-to-back surge. They do little for side-to-side movement.
- A partly filled tank is often the worst handling case: enough weight to push, enough space to slam.
Rollover control
High center of gravity plus side surge means the trailer leans outward in a curve. Slow down before the curve, keep steady throttle through it, and avoid braking or steering sharply mid-curve. Make lane changes gently and one at a time.
Braking and downgrades
Stopping distance is longer and brake fade comes sooner. Select a low gear before the grade, use engine braking, and apply brakes firmly rather than fanning them.
Worked example
A 5,000-gallon tank is about half full approaching a ramp rated 25 mph. The driver enters at 40 mph and the liquid surges to the outside of the curve, lifting the inside wheels. The correct response is to slow below the advisory speed before the ramp and hold steady through it - braking hard inside the curve makes the rollover more likely.
Traps that cost marks
Claiming baffles stop surge. Coasting downhill in neutral. "Using momentum" to climb a grade at speed. Overcorrecting after a lane change.