For my Chartiers Branch S-scale layout I needed two steel plate girder deck bridges. The vast majority of the 19 bridges on this Branch were of this type, so I have to model at least a few. All of them are built on top of cut-stone abutments. People have indicated that there was usually about 10ft (3m) of clearance under the bridges. All the bridges appear to have an open floor (as opposed to a ballasted floor). Since a significant amount of the Chartiers Branch was double-tracked (especially during the time I model), the abutments and piers appear to be wide enough to hold two tracks. The picture below is very representative of the plate girder bridges I have found on the Web (this photo came from one of the members of the "prr_panhandle_pa" Yahoo Groups).

1. The Abutments - 02/12/2009

2. The Bridge (version 1 - 02/12/2009)

3. The Bridge (version 2 - 04/07/2009)

4. The Bridge (version 3 - 04/04/2012)