I was in the South Boston area in the summer of 2004 when VDOT came very close to demolishing this bridge. I went for a drive one Sunday afternoon looking for the Clarkton Bridge and when I found it there was a gathering of supporters to save the bridge. I took many pictures and followed the newspapers for months to see what happened to the bridge. I'm glad to know it is still standing and I hope I can visit it again someday.
Those are called "trussed beams". It is a concept similar to truss rods under old-fashioned wooden railroad cars. It looks, from the pictures, that these were added in on after the bridge was built.
This bridge has perhaps the most unusual floor beams that I have ever seen. They are what I know as "Fishbellies" but are not a solid beam.