At first (before magnifying glass)I thought it might be an old rail. But with the glass it does look like two 2x6 on edge, centered betweend the rails. I can see a joint in the near piece, and can just barely see the ends. It looks like it runs into the blacktop. I've worked on a few crossings before, and put form boards over closer to the rails, and once protected some conduit with a tunnel made of wood, but very much deeper than this. ?