A cross-platform interchange is a type of interchange between different lines at a metro (or other railway) station. The term originates with the London Underground; such layouts exist in other networks but are not commonly so named. In the United States, it is often referred to as a "cross-platform transfer". This configuration occurs at a station with island platforms, with a single platform in between the tracks allocated to two directions of travel, or two side platforms between the tracks, connected by level corridors. The benefit of this design is that passengers do not need to use stairs to another platform level for transfer, thus increasing the convenience of users. A cross-platform interchange arrangement may be costly due to the complexity of rail alignment, especially if the railway designers also arrange the track with flyovers (which is typically done to increase efficiency). A common two-directions cross-platform interchange configuration consists of two directions of two different lines sharing an island platform, and the respective return directions of both lines sharing a different island platform in the same station complex. Much rarer is a cross-platform interchange to transfer onto the same line as in Kirkby and Ormskirk.