What is the primary function of the signal at DLB SX 988.1 for southbound trains?

The signal at DLB SX 988.1 for southbound trains primarily serves the function of allowing trains to pass safely by indicating that the track ahead is clear and that it is safe for the train to proceed. This is crucial for maintaining efficient train operations and ensuring the safety of all rail traffic within that segment. Understanding the role of signals, especially in determining movement authority, is essential for conductors, as it directly impacts scheduling and operational flow.

The other options suggest different functions that signals might serve; however, in this context, the specific purpose of allowing trains to pass aligns most accurately with the operation at DLB SX 988.1. Such clarity in signal indications helps manage train movements effectively, reducing the risk of incidents or delays.