Overpass or bypass[1]​[2]​ is the process of adapting a junction of two or more transportation axes at different heights ("Slope (geography)") so as not to disrupt the flow of traffic between other transit routes when they cross each other. The composition of these transport axes does not have to be uniform, but can consist of a mixture of roads, trails, railways, canals or airport runways. Tunnels, bridges, viaducts or combinations of these can be built at a crossing to achieve the necessary degree of separation.