When can truck drivers and passengers remain in their vehicles?

The correct answer is based on safety protocols specified in the USACE EM 385-1-1 guidelines. Passengers and truck drivers are permitted to remain in their vehicles unless instructed otherwise by an authorized person. This regulation is designed to ensure safety in potentially hazardous situations, such as those involving heavy machinery or when working in environments with specific risks. The presence of an authorized person indicates that there may be a need for action to mitigate risk, and therefore, staying in the vehicle without direction could expose individuals to unnecessary danger.

The rationale emphasizes the importance of following orders from designated personnel who are trained to assess the safety of an area and make decisions accordingly. It keeps all individuals out of harm's way until it's verified that it is safe for them to exit their vehicles. This rule aligns with safety management practices where maintaining communication and following directives from a leader or supervisor is critical during operations.