The bridge spans are 385 feet, 510 feet, and 305 feet. When it was built, it was the longest plate girder bridge in the world. A plate girder is much like a standard girder, but rather than use I-beams, the beams are built up from plate steel. In this case, a long narrow piece of steel plate is cut. The width of the plate depends on the type of weight that it has to carry. The plate will be wider near the piers, and narrower in the middle. From there, narrow strips of steel plate are welded to the edges of the main plate, and stiffeners strips are welded to the top and bottom of the plates. This forms a custom made plate girder beam. This bridge uses 7 parallel plate girders. The 510 foot long main span is an amazing length span without having a large truss or suspension cables.
Note that the last two photos below show parts of the old truss bridge that was removed in 1981 are still on site in the park on the south end of the bridge. They are decorated as pieces of pop art.
The original US Government highway test site was located near Ottawa along what is today I-80. Former military personnel drove heavily loaded trucks in shifts of 12 hours a day from 1858 to 1960 to determine if the base design and pavement selected for the Interstate highway system would hold up over the long term. Over 17-million miles were logged on the test road.