Bridge Roadbed

(or bridge floor), the upper structure of a railroad line on a bridge; the part of a railroad bridge that directly receives the force effects from the wheels of a train and transmits them to the superstructure of the bridge. The roadbed may be on ballast or crossbeams.

Roadbeds on ballast are used on small bridges, overpasses, and reinforced-concrete bridges, and also on bridges located on curved portions of a line or on a grade. In this case the railroad tracks are fastened to wooden or reinforced-concrete sleepers that are laid on gravel ballast. Roadbeds on crossbeams are used mainly on metal bridges; the tracks are fastened to wooden crossbeams (bridge beams) that are laid on the longitudinal or main beams of the superstructure and attached to them by special bolts.