What is liquid surge and why is it dangerous when driving a tanker?

LIQUID SURGE: The movement of liquid in a partially filled tank. When the tanker slows or stops, the liquid moves forward in a wave, then back — this surge can push the truck forward (even after the driver has stopped braking) or affect control. DANGER: Surge can push a stopped tanker into an intersection; it makes the vehicle harder to control during braking, turning, and lane changes; the wave action can affect steering; SMOOTH driving is essential — gradual braking and acceleration, no sudden moves; allow extra stopping distance; be especially cautious on slippery roads and when stopping; BAFFLES: Many tanks have baffles (bulkheads with holes) that reduce front-to-back surge, but NOT side-to-side surge; some tanks (like those for milk/food, which must be cleaned easily) are SMOOTH BORE (no baffles) and have the most surge; surge is a defining hazard of tanker driving and requires constant awareness and smooth operation.