Where may permission to pass a stop signal not be issued to a TC via Form D line 3?

Permission to pass a stop signal is critical in maintaining safety and operational integrity on the railroad. The correct situation where permission may not be issued to a Train Crew via Form D line 3 is at the initial or final interlocking. Interlockings are complex junctions where tracks cross or converge, and because they are designed to protect movements through critical areas of the railroad, issuing permission to proceed past a stop signal in such zones could lead to serious safety hazards.

At an interlocking, signals control the movement of trains and ensure that routes are set safely, preventing potential conflicts. Allowing trains to pass stop signals here without oversight could lead to incidents involving other trains or obstructions.

In contrast, other locations like highway crossings, inside yard limits, or at the main station typically have protocols and safety measures that allow for certain operational flexibility. However, interlockings are specifically designated as areas where strict adherence to signal indications is paramount. Therefore, the prohibition of passing a stop signal at interlockings upholds the safety standards that govern railroad operations.