(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.
N. N. BOGDANOV