Modular and prefabricated bridges are traffic spans that are partially constructed at an off-site location before transportation to the installation site; this is opposed to transporting all materials to the worksite and then erecting the structure. These designs are highly adaptable and suitable for many span lengths due to their ease of assembly and relative inexpensiveness. The industry of modular bridgebuilding originates from the pontoon construction of spans to help armies cross bodies of water that predates industrialized warfare; this is a need of modern militaries as well.
Sections of the bridge typically have mating components that are raised and then secured by ironworkers. Prefabricated bridges are especially prevalent for spans that cross water or highways as methods (i.e. barge, road train) of configuring heavy components in their final position are already in place. The term prefabrication does not account, nor necessarily preclude, for the existence of bridge components before a work order. However the comparable construction of many prefabricated bridges greatly reduces installation time required and their nature still allows engineers to account for design peculiarities.