Metaphorically a bottleneck is a section of a route with a carrying capacity substantially below that characterising other sections of the same route. This is often a narrow part of a road, perhaps also with a smaller number of lanes, or a reduction of the number of tracks of a railway line. It may be due to a narrow bridge or tunnel, a deep cutting or narrow embankment, or work in progress on part of the road or railway. Capacity bottlenecks are the most vulnerable points in a network and are very often the subject of offensive or defensive military actions. Capacity bottle necks of strategic importance - such as the Panama Canal where traffic is limited by the infrastructure - are normally referred to as chokepoints; capacity bottlenecks of tactical value are referred to as mobility corridors.
