LevelCodeValue The route is at the same level as the surrounding terrain. Surface Level The RouteLink is supported or suspended above ground level on a manmade structure. For example, a road, track or path may be on a bridge, footbridge or viaduct. Above Surface Level On Structure The route passes through a specially built construction underneath the normal terrain surface primarily to avoid or reduce the effect of the terrain surface or to avoid an obstruction such as a river or mountain. Below Surface Level Tunnel