Under which condition can the speed be increased when a yellow-red flag is present?

The scenario describes a situation where a yellow-red flag is present, which typically indicates a restriction or caution for train operations. Under these circumstances, the key factor for safely increasing speed is the communication from the employee in charge. If a crew member receives clear and direct instructions from the designated authority, such as the employee in charge, this establishes that necessary precautions have been taken and ensures that the crew is operating under the guidance of someone with oversight and authority.

In this case, having instructions from the employee in charge indicates the crew is authorized to adjust their speed, likely after verifying that it is safe to do so. This process promotes safety protocols and adherence to communication standards critical in railway operations.

The other conditions, while relevant to train movements, do not inherently provide the same level of assurance regarding safety and authority needed to increase speed when a yellow-red flag is present. Therefore, receiving specific instructions from the employee in charge is paramount to ensuring that the speed increase aligns with operational safety guidelines.