Can you point out where you see timber beams in the photo? I can't even find a place where they would go; to me the deck looks like pour-in-place unreinforced concrete that sheared right off at the piers; the deck is then covered in what looks like gravel (which also seems a bit bizarre), then a wooden guardrail on wooden posts is bolted into the concrete deck.
The bridge looks to be precast concrete box-girders (hollow rectangular beams with plenty of steel reinforcement around the edges). The 'gravel' is the asphalt roadway (often this will be cast-in-place concrete) that's poured on top of the precast girders. The purpose of pouring the asphalt/concrete roadway on top is as a sacrificial wear element to prevent the structural beams being worn down by traffic.
