Railway signals serve a similar purpose to that of traffic signals for cars on roads. In fact; road signals were developed from railroad signals, not the other way around.

When driving a car, the yellow/amber light appears for a few seconds before the red light appears as a warning to prepare to stop (note: road traffic laws vary from country to country so the exact meaning of a yellow/amber signal may vary depending on where you live). On a road the yellow/amber signal could be timed depending on a number of factors such as the volume of traffic and/or prevailing speed on the road the signal governs. The timing of the yellow/amber signal phasing is likely to take into account probable stopping distances for cars and trucks on the particular road.

Unlike trains, cars and trucks don’t take as much time or distance to stop. The other difference is that cars and trucks can change direction to avoid a crash. That is why the yellow/amber warning light on road signals can be located on the same signal apparatus as the red danger light.

Trains, however, are heavy and take considerable time and distance to stop. Trains may require from half a mile, to a mile and a half to come to a complete stop. This is why, trains need a warning signal well before the point where they have to stop. That is one of the biggest differences between train signals and road signals.