Bridges presentation
the massive weights of the bascule, lift, or swing spans marked the beginning of modern moveable-
bridge construction. They are usually found in flat terrain, where the cost of approaches to gain
high-level crossings is prohibitive, and their characteristics include rapidity of operation, the ability
to vary the openings depending on the size of vessels, and the facility to build in congested areas
adjacent to other bridges.
Completion of Tower Bridge over the Thames in London (1894), a 260ft (79m) roller-bearing
trunnion bascule and the best known bascule bridge in the world, and Van Buren Street Bridge in
Chicago, the first rolling lift bridge in the USA (patented by William Scherzer), marks the efficient
solution to problems of lifting and locking mechanisms. In 1914, the Canadian Pacific Railroad
completed the world's largest double-leaf bascule, spanning 336ft (102m) over the ship canal at
Sault-Sainte-Marie, Michigan, rebuilt with identical spans in 1941
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