What is a signal aspect and what do green, yellow, and red indicate?

• A. The visual state of a signal conveying the status of the next block; green means proceed, yellow means proceed with caution or prepare to stop, red means stop.
• B. A device that reports weather at the station.
• C. A type of track circuit.
• D. A system for logging maintenance data.

Answer: (A)

Signal aspect is the visible display on a signal that communicates the status of the block of track ahead to the train driver. Green means the next block is clear, so the train may proceed at normal speed. Yellow means proceed with caution and be prepared to stop at the next signal (or slow to a restricted speed, depending on the system). Red means stop, as the block ahead is not available. These colors provide the driver with immediate, interpretable guidance to maintain safe distances and proper speeds. Other options describe unrelated devices or systems, such as weather reporting, track circuits, or maintenance logs, which are not what a signal aspect conveys.