What does this mean?

[jettrainfan]

Today and other times, i have been seeing signals flash a yellow light on and off! What does it mean? it is between west 117th station and trisket station. that is the only area i have seen this.

[jward]

if it was only a flashing yellow, on some railroads this is a fourth basic signal indication. it is between a clear signal (green) and a ye;;ow (approach) in the hierarchy.

if it was a red over flashing yellow, that is called a limited approach. it usually indicates you are going to take a high speed crossover, but the next signal is stop.

in both cases, the flashing means you are allowed to pass the signal at a higher speed than a normal steady yellow.