This style truss bridge is called a continuous truss as opposed to a simple truss. A simple truss has two piers, one at each end point. A continuous truss has 3 or more piers. In the case of the Lacon Bridge, it has 4 piers, one on each end, and two mid-channel. The continuous truss bridge is one rigid structure that spans more than 2 piers. In contrast, we often see simple trusses mounted back to back across 4 to 6 piers, as in the Henry Bridge just up stream. The continuous truss can be built with longer main channel spans than simple truss bridges, so they are used in cases where you want a wide navigation channel. There are many continuous truss bridges over our major rivers, but they have the disadvantage that they are costly to maintain. As a result, new bridges are being built using the cable stayed method (like the Clark Bridge in Alton) or the post-tension concrete segment method (like the new I-35W Bridge in Minneapolis).