Viaduct came into play because, each of the what most people would call "concrete bents" are in this design and specs, called abutments, thus the make a series of small spans, and they only cross land (no water), thus matching pretty closely this definition of a viaduct:

"A viaduct is a bridge composed of several small spans for crossing a valley or a gorge. The term is conventional for a rail flyover as opposed to a flying junction or a rail bridge which crosses one feature. In Romance languages, the word viaduct refers to a bridge which spans only land. A bridge spanning water is called ponte.