Railroad tracks appear to converge due to our field of view. When an object is far away it seems smaller that means there is angle that subtends from our line of sight this results in the illusion of railroad tracks converging.
Railroad tracks converging activates the linear perspective of our vision. Linear perspective is a technique used to convey a sense of depth in two dimensional representation of an object. The lines at an angle give us a sense of depth otherwise straight lines will not be able to convey depth.
