What must a control operator do before authorizing a train to proceed past a stop signal?

The correct choice emphasizes the critical safety protocols that a control operator must follow before allowing a train to proceed past a stop signal. The control operator must ensure that the route is clear of any obstructions and that there are no conflicting movements from other trains or equipment in the vicinity. This is vital to prevent potential collisions and to maintain safe rail operations.

Checking if the route is clear is an essential part of the signaling and safety system in rail operations. It involves assessing track occupancy, analyzing traffic signals, and coordinating with other operational staff to ensure a seamless flow of trains. This preventive measure is fundamental to railway safety, ensuring that each train can proceed without the risk of encountering obstacles or other trains that could lead to accidents.

The other options, while they touch on important aspects of operational readiness, do not directly address the immediate and critical concern of route safety when a train approaches a stop signal. Fuel levels, crew alertness, and written reports are all important elements of overall operational safety and efficiency, but they do not directly impact the clearance for a train to move past a stop signal.