Swing bridge

A swing bridge is a bridge that has as its primary structural support a vertical locating pin and support ring at or near to its center, about which it can then pivot horizontally as shown in the animated illustration below. Small swing bridges as found over canals may be pivoted only at one end, opening as would a gate, but require substantial underground structure to support the pivot.
In its closed position, a swing bridge carrying a road over a river or canal, for example, allows road traffic to cross. When a water vessel needs to pass the bridge, road traffic is stopped, and then motors rotate the bridge approximately 90 degrees horizontally about its pivot point.