An orbital (also known as a circle line or loop) in the context of metro systems is a metro or subway line encircling a city or metropolitan area. Such lines relieve the loads on other lines within the orbital by providing alternative connections among the other lines. In other words, a passenger whose origin and destination are both outside the enclosed central area but on different lines can bypass the urban center and possibly shorten the journey by going around the (often congested) area enclosed by the orbital.