Which of the following can cause a dumper to tip over sideways during travel?

A dumper tipping over sideways during travel is primarily influenced by uneven surfaces and obstacles that disrupt its stability. Deep potholes can be particularly harmful as they create sudden drops that can lead to an imbalance. When a dumper hits a deep pothole, one side of the vehicle may drop significantly while the other remains elevated, which can shift the center of gravity and cause the dumper to tip over.

Driving on a flat surface typically promotes stability and control, while low tire pressure affects overall vehicle handling but is less likely to cause an immediate sideways tip compared to the abrupt change in terrain presented by deep potholes. Using safety barriers is designed to enhance safety and prevent accidents rather than contribute to tipping. Thus, the presence of deep potholes directly contributes to the risk of a sideways tip, making it the appropriate answer.