A cargo tank motor vehicle must not be operated under which of the following conditions?

A cargo tank motor vehicle must not be operated where it can cause an accident or breakdown because safety is of utmost importance when transporting liquefied petroleum gas. Operating a vehicle in a location or condition that poses a risk can lead to hazardous situations, potentially resulting in spillage, fire, or explosions. This principle aligns with NFPA 58 guidelines, which prioritize the safe transportation of LPG to prevent incidents that could harm individuals, property, or the environment.

In contrast, performing routine maintenance checks or inspections is a standard practice that ensures the vehicle is safe and compliant with regulations. Adverse weather conditions might pose risks, but there are scenarios where operations can still continue safely with appropriate precautions. Thus, the focus is on the overarching principle of avoiding any situations that increase the likelihood of accidents during operation, which is why the identified condition is critical.