bascule bridge
A movable bridge with one or two leaves that rise on hinges with assistance from counterweights.
A bascule bridge is an openable bridge whose span rises by turning on a hinge with the aid of a counterweight. It may have a single leaf hinged at one end, or it may consist of two leaves that meet in the middle, each with its own hinge at the shoreline or riverbank. This is one of the most common types of movable bridges, especially on city streets.
Each opening leaf turns about its hinge, aided by a counterweight. One leaf can cover the crossing, or two opposed leaves can meet near the center.
Counterweight assistance distinguishes this form from the separately defined drawbridge lifted at its free end. A rolling bascule instead uses rolling support without a fixed hinge.