As guessed by everyone, those are indeed Atlas Deck girder bridge sections with the sloped ends cut off. The deck on it is Central Valley bridge ties sets.
I'll ask the photographer. We are in the same model railroad club. I would agree though that it appears to be parts from the atlas deck truss kit. The deck on the bridge may be from a source other than atlas. Ill either post here or PM the op with the answer.
Very nice modeling, both bridge and river. I, too, recognize the Atlas lineage in the trusses.
To the OP - a deck GIRDER bridge has a solid sheet of steel, reinforced with angle braces, where the illustrated model has that open lattice. To a civil engineer, there is a difference.
Chuck (Modeling Central Japan in September, 1964 - with lots of oxide red deck girders)
Those are almost certainly Atlas deck truss bridges with the angled end portions cut off. See http://www.modeltrainstuff.com/Atlas-HO-Code-83-Deck-Truss-Bridge-Kit-p/atl-591.htm .
Rob Spangler
I have a two similar bridges on my layout, mine are Atlas Deck Truss bridges. One is exactly as purchased and the other has been "Kit Bashed" into a longer span by snipping off the end diagonal pieces and joining to a second length of the same Deck Truss bridge. Closely examining the photo on page 88 of the referenced issue of MR would lead me to believe that Mr. Murphy did the exact same thing with his bridge, using the Atlas Deck Truss kits, as I can see the splices between the kits, above the concrete piers.
NP 2626 "Northern Pacific, really terrific"
Northern Pacific Railway Historical Association: http://www.nprha.org/
Why not ask MR directly? I'm sure they can contact the author and, with his permission, they might actually be able to put you in touch with him.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Prototype research has led me to an interest in deck box girder bridges for my layout. The one in Trackside Photos on p. 88 of the Jan. 2015 MR matches what I'm looking for perfectly. Is it a kit? Kitbashed? I'd love to know more.
Searching the HO Walther's website gives me a few European designs (not the look I'm after) as well as an Atlas bridge that would require some chopping. Similar results for N scale.