Final answer:
The large size of a train can create an optical illusion that makes it appear to be moving slower than it actually is.
Step-by-step explanation:
The phenomenon described in the question is an example of relative motion. When an object is large, like a train, its size can create an optical illusion that makes it appear to be moving slower than it actually is. This is known as the size-distance relationship. An example of this is when a fast-moving train looks slower when observed from a distance.