Truss bridges are characterized by the joining of numerous relatively small structural members into a series of interconnected triangles. They were first built of wood, then iron, then steel or occasionally a combination of the materials which underwent an explosion of design and technological innovations that began in the mid-19th century.

A truss bridge can be characterized by the location of its traffic deck. On a pony truss, the travel surface passes along the bottom chords of trusses standing to either side that are not connected at the top. These trusses are designed for lighter loads.

On a through truss bridge, the deck again is carried along the bottom chord, but the trusses to either side are generally higher and are connected by cross-bracing at their tops. Designed for heavier loads and longer spans, this truss is the most common.

The least common is the deck truss, which carries its deck and traffic entirely on top of the truss structure.

Metal trusses can also be differentiated by how their structural members are connected. The earliest examples were connected with pins. The pin connection was subsequently replaced by bolted and then welded connections.

Currently there are a total of five eligible state owned Truss bridges left in the state. They are as follows:

1. S-159 (Millers Mill Road) Bridge in Abbeville County - A Pony Truss
2. S-42 Bridge in McCormick County - Through Truss
3. SC 23 Bridge in McCormick County - Pony Truss
4. S-117 Bridge in McCormick County - Through Truss
5. S-32 Bridge in Oconee County - Pony Truss