... bridge with a middle section of the roadway that swings around a central pier to open up a passage for travel. Lift: A type of moveable bridge which works like an elevator; the roadway, which is attached to two columns, raises up vertically to allow for passage underneath. Bascule: A type of moveable bridge, which acts like a seesaw, allowing sections of the bridge to be lifted using weights as a counterbalance. General history of bridges Bridge technology was modernized during the first half of the twentieth century. Older highway bridges were commonly steel truss structures, but with improvements in concrete and composite steel and concrete design, the massive truss structures began to disappear. Concrete proved to be an adaptable material and was suitable in arched bridge designs or in post and beam construction over short spans. Prior to 1920, most bridges accommodated only one lane of traffic. Motorists travelling at high speeds did ...

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