Abstract: A bridge construction system includes a first independent longitudinal truss positioned over a first bridge span, a second independent longitudinal truss positioned over a second bridge span, a gantry movably mounted on said trusses, the gantry having a first leg mounted to the first truss and a second leg mounted to the second truss, the gantry being drivable along the first and second trusses, a gantry drive for controllably driving the gantry along the trusses, a transverse trolley movably mounted on the gantry, the trolley being drivable along the gantry in a direction generally transverse to the longitudinal trusses, the trolley including a winch for lifting and carrying bridge components to be positioned along the bridge spans over which the longitudinal trusses are mounted, the trolley being selectively positionable over each of the bridge spans, and supports for mounting the longitudinal trusses to bridge components disposed along each of the bridge spans.