The humps in the middle of the Interstate Bridges are two of the reasons that proponents of the Columbia River Crossing point to when explaining why a replacement bridge with a light rail line is the most pressing transportation need that merits $450 million, plus interest, of Oregon's tax dollars. The interesting thing about the humps is that they were built not as a problem but as a solution.
The original Interstate Bridge (what is now the northbound bridge) had a drawspan, but no humps. The road was level. When the southbound bridge was built in the 1950s, the highway department wanted to reduce the number of bridge lifts, and built the southbound bridge with a hump, under which some river traffic could go without requiring a bridge lift. When the southbound bridge opened, the northbound bridge was closed so that a matching hump could be added.
The basic problem with the project, and a possible solution, occurred to me a few days ago, and I'll share the problem and the solution this week.