Because much of a tanker's load rides high above the road, the vehicle is top-heavy and can roll over easily. The other concern is surge: liquid moving inside a partly filled tank can push the vehicle when you brake, accelerate or turn.
Weight in the tank pushes the tires harder against the road, which improves their grip. Without that weight the tires hold less well and lock more easily, so an empty tanker can actually need more room to stop than a loaded one.
An empty truck has little weight pressing its tires onto the pavement, so it has less traction, and its stiff springs and strong brakes can lock the wheels more easily. For those reasons it can take more distance to stop than a truck carrying a load.
Tankers call for extra care because their load rides high and because the liquid can slosh inside the tank, and that movement can shove the vehicle and help tip it over in a turn or sudden maneuver. A tanker's center of gravity is high, not low, and the sheer weight of the cargo is not one of the two reasons.
Liquid cargo calls for special skill for two reasons: a loaded tanker has a high center of gravity, and its contents can slosh in any direction while you drive. Uneven expansion and excess weight are not among those reasons.
Finishing your slowing before the curve and then adding a little power through it keeps the tanker stable and its load settled, which lowers the risk of a rollover. Braking in the curve makes it easier to lock the wheels and skid, and coasting in neutral takes away the control that engine power gives you.
Tank vehicles are top-heavy because much of the cargo's weight rides high above the road, so they can roll over even at the speed posted for a curve. Also keep in mind that an empty tanker may need more distance to stop than a loaded one, not less.
Much of a tanker's load weight rides well above the pavement, which makes the vehicle top-heavy and quick to roll over; tests have shown tankers can tip over even at the speeds posted for curves. That high center of gravity is a main reason liquid loads demand extra care.
Liquid sloshing in a partly filled tank strikes the end of the tank and shoves the truck in the direction the wave travels. This can upset braking and steering on any surface, though the danger is greatest on slick roads.
In a partly filled tank, a heavy mass of liquid can slosh around, and its momentum pushes on the vehicle. A wave rolling forward as you brake can push the truck ahead and lengthen your stop, while a wave rolling sideways in a turn can help tip it over.
When a tank is not completely full, the cargo has room to rush forward, backward or sideways as the vehicle moves, and this shifting is called surge. When the moving liquid reaches the end of the tank, it can push the vehicle in the direction the liquid is traveling.
When you brake, the liquid rushes toward the front of the tank and its force shoves the truck ahead. On ice or another slick surface the tires cannot resist that push, so even a stopped truck can be driven into another vehicle or out into an intersection.
Baffles can slow liquid moving toward the front or rear, but they do little to stop it from sloshing sideways. A sharp turn while braking throws the cargo to one side, and that sudden shift of weight can tip a top-heavy tanker over.
Slowing down early and gradually, with the same pedal pressure all the way, keeps the liquid from building into waves. Hard braking, or letting up on the brakes too soon, makes the load slosh and shove the truck.
A tanker's high center of gravity means it can overturn on a curve even when the driver stays at the posted speed, as testing has shown. Slow to a speed well under the posted figure for curves, on-ramps, and off-ramps.
Liquid sloshing toward one side moves the tanker's weight and its high center of gravity sideways, and on a curve or during a quick lane change that shift can tip the vehicle over.
To keep the liquid from slamming back and forth, begin slowing long before the stop, hold the pedal pressure even until the vehicle is stopped, and leave a bigger gap ahead. Fast steering movements during braking can tip a tanker over.
A tanker is top-heavy because much of its load rides high above the road, which makes rollovers more likely. In a partly filled tank the liquid also surges, and that moving weight can push the vehicle forward, backward or to the side.
Hitting the brakes during a sudden turn can easily lock the wheels, and a vehicle with locked wheels may slide out of control. Keep braking and swerving separate, and remember that no single direction is right in every situation.
Turning the wheel and braking at the same moment makes it very easy to lock the wheels and slide out of control, and a tanker's shifting liquid load makes that even riskier. Steer only as much as you need to clear the hazard, and do not brake during the turn.
Every question in this set has its own page with the correct answer and an explanation.
