What time must trains be available for passenger boarding?

The correct answer indicates that trains must be available for passenger boarding immediately upon completion of preparation procedures. This requirement ensures that the train is ready and safe for passengers to board as soon as it has been properly prepared. Timely availability is crucial for maintaining the schedule, ensuring that departures occur as planned, and providing a smooth and efficient transit experience for passengers.

If a train were to be available later or at the discretion of crewmembers, it could lead to delays and affect the overall reliability of service. Timely readiness helps manage passenger expectations and keeps the transit system running smoothly. Being ready immediately after preparation reinforces the importance of efficiency and operational discipline within the transit system.