Tank vehicles are more likely to roll over because of liquid movement and _________.

Hauling liquids in tanks requires special skills because of the high center of gravity and liquid movement. A high center of gravity means that much of the load's weight is carried high up off the road. This makes the vehicle top-heavy and easy to roll over.
Liquid tankers are especially easy to roll over. Tests show that tankers can turn over at the speed limits posted for curves. Take highway curves and on-ramp/off-ramp curves well below the posted speed limits.