Under the deck of a reinforced concrete single span overcrossing (a bridge over the highway) is what I would call a structural steel space truss. It's made up of eight-legged elements connecting the concrete slab to longitudinal and transverse steel elements. Apparently, these thin elements are strong enough to increase the bending resistance of this structure.
This type of structure is apparently very popular in Colima. There is a water main supported by a similar structure 140 ft away, and single span and two span bridge undercrossings (a bridge carrying the highway) a few miles to the north.
Mexico's Bridges: Overcrossing near Tonila by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.