Flat car for railway freight unit loading

Claim 1

A RAILWAY CAR OF SINGLE LONGITUDINAL BEAM DESIGN ADAPTED FOR USE IN PIGGYBACK OPERATION, SAID CAR COMPRISING A CENTER LONGITUDINAL BEAM PORTION HAVING WHEEL TRUCKS MOUNTED THEREBENEATH, SAID CENTER BEAM PORTION INCLUDING A LONGITUDINALLY CONTINUOUS TOP COVER PLATE FIXED THERETO, CROSS BEARER MEANS SPACED LONGITUDINALLY OF SAID CENTER BEAM PORTION AND PROJECTING RADIALLY OUTWARDLY THEREFROM ON EITHER SIDE THEREOF IN FIXED ATTACHMENT THEREWITH, A LONGITUDINALLY CONTINUOUS UPSTANDING SIDE SILL FIXED TO THE OUTER ENDS OF SAID CROSS BEARER MEANS TO EACH SIDE OF SAID CENTER BEAM PORTION AND LONGITUDINALLY CONTINUOUS FLOOR PLATES SPANNING THE TRANSVERSE SPACE BETWEEN SAID CENTER BEAM PORTION AND SIDE SILLS AND FIXED TO SAID CENTER BEAM PORTION AND SAID SIDE SILLS, SAID FLOOR PLATES BEING RECESSED BELOW THE TOP SURFACES OF SAID COVER PLATE AND SIDE SILLS TO DEFINE RELATIVE THERETO WHEEL TRACK AREAS WITH THE PROJECTING TOP PORTION, SIDE SAID CENTER BEAM PORTION AND SIDE SILLS PROVIDING WHEEL GUIDE SURFACES, THE MASS OF SAID CENTER BEAM PORTION, SIDE SILLS, FLOOR PLATES AND COVER PLATE BEING SELECTED AND LOCATED TO ESTABLISH A SINGLE NEUTRAL AXIS FOR THE CROSS SECTION OF SAID CAR, WHICH NEUTRAL AXIS IS LOCATED SO THAT SAID FLOOR AND COVER PLATES AND SAID SIDE SILLS FUNCTION IN THEIR ENTIRETY AS THE TOP COMPRESSION CHORD OF SAID SINGLE LONGITUDINAL BEAM DESIGN.