What must happen if blocking devices are applied and TC has not cleared an interlocking?

When blocking devices are applied, they serve to ensure safety and prevent unauthorized access or movement into areas where trains may be operated or where workers may be present. If the Train Controller (TC) has not cleared an interlocking, it indicates that the tracks are still considered occupied or unsafe for use.

In this context, the correct answer highlights that the blocking devices must remain until the TC is clear of the interlocking. This is essential for maintaining safety on the rail network. By leaving the blocking devices in place during this period, it ensures that no train movements can occur that would put personnel or equipment at risk. The blocking devices act as a physical reminder of the potential hazards and serve as a safeguard against possible accidents.

The removal of blocking devices would only be sensible once the interlocking is confirmed to be clear and safe, aligning with protocols that prioritize safety over operational convenience. Hence, the requirement to keep the devices until the TC is clear of the interlocking is a fundamental safety measure in rail operations.