As the railroads expanded, railroad bridges were erected to enable lines to follow the most direct routes possible. Engineers devised a range of architectural and engineering strategies for overcoming the obstacles of local geography—from vaulting brick viaducts spanning valley floors to iron suspension bridges that dangled tracks above rivers and gorges. Concrete and steel are now the materials of choice, but the ingenuity of modern designs is no less impressive than the elegant blends of function and form deployed by the early railroad builders.
The Tangiwai disaster
New Zealand’s worst ever rail bridge disaster occurred on Christmas Eve, 1953, when 151 lives were lost in the catastrophic failure of the Whangaehu River bridge near Tangiwai, in the center of the North Island. A mudflow from a collapsed dam destroyed a supporting pier of the beam bridge (see panel, below), which gave way under the weight of an express train.
Types of bridge
Different types of railroad bridges have been developed to meet geographical and economic constraints. While there are multiple variations on—and combinations of—each design, the basic types of bridge can be grouped into four categories: beam, arch, cantilever, and suspension.