What does the term "restricted speed" refer to in train operation?

The term "restricted speed" in train operation specifically refers to a speed that allows a train to stop within half of its range of vision. This definition is crucial for ensuring safety in areas where visibility is limited or where there may be irregularities on the track. When a train operates at restricted speed, it is able to respond to potential hazards, such as obstructions or signals, with sufficient time to stop safely, thus preventing accidents or collisions.

Understanding this concept is essential for train operators, as it underlines the importance of adjusting speed based on environmental conditions and track conditions to maintain safe operations. The other choices cover different aspects of train operations but do not capture the specific definition of restricted speed.