The primary use of rail transfer bridges is to span from floor to floor or dock to dock over railroad tracks. The platforms are left in the horizontal position most of the time and then elevated to the vertical position when trains need to pass on the railroad spur. In the most common application there is a single bridge recessed in the face of one floor or dock and when the bridge is lowered, the traveling end of the platform rests in a recess on the opposing dock. Sometimes due to overhead clearance problems or very long spans, two bridges are positioned end to end, each hinged on opposing docks so that their traveling ends meet in the middle of the span. In these instances, the traveling ends of the bridges are either supported by a concrete pier or each bridge leaf is equipped with automatic folding legs.