Vertical-lift bridge

A vertical-lift bridge or lift bridge is a type of movable bridge in which a span rises vertically while remaining parallel with the road surface.
The vertical lift offers several benefits over other movable bridges such as the bascule and swing-span bridge. They are generally easier to design and easier to build. They usually cost less to build for longer moveable spans. The counterweights in a vertical lift bridges are only required to be equal to the weight of the deck. Bascule bridge counterweights must weigh several times as much as the span being lifted. As a result, heavier materials can be used in the deck, and so this type of bridge is especially suited for heavy railroad use.
Although most vertical-lift bridges use towers, each with counterweights. Some use hydraulic jacks located below the deck. An example is the span bridge at St Paul Avenue in Milwaukee, Wisconsin, USA. Another design used balance beams to lift the deck with pivoting bascules located on the top of the lift towers. An example of this kind is the La Salle Street Bridge in Chicago, Illinois, USA.
The biggest disadvantage to the vertical-lift bridge is the height restriction for ships passing under it. This is a result of the deck remaining suspended above the water.