The construction appears to have been I beams encased (perhaps later) in concrete. The voids in the concrete make me wonder if it was placed after the track was active and they had some trouble getting the concrete properly tamped into the form.
A quick visit locates the old bridge. Great information, Kelly!
Actually, the old bridge is still there, it is just hard to see due to the over growth in the area. Granted, line was cut, but about a hundred yards south of the old bridge. If the line is ever reopened (which is doubtful) the City of Raytown would have to put in a bridge, which would require the line being raised about a mile in either direction.