The Interstate Bridge is operated and maintained by the Oregon Department of Transportation with half the funds for operation coming from Washington State Department of Transportation. If fact, one my uncles use to work on the ODOT maintenance and operation crew on the Interstate Bridge.
There has been a major study for the replacement of this bridge going on for numerous years, but no determination as to bridge type or a timeline has been made to date. I do believe the preferred alternative for the bridge is a deck truss structure, but that could have changed since I last checked out the project. Anyone interested can check out the progress of these studies and meetings by clicking on the link for the “Columbia River Crossing” at the bottom of the bridgehunter page.
At this point in time, I personally do not see this bridge getting replaced in the next 5 years. The feds, the two states, along with all of the local interests might get a project put together for construction around 10+ years out, but that is still optimistic after seeing how communication between all the interested parties has gone thus far.
This landmark bridge appears to be slated for demolition and replacement. Guess its more a Washington state bridge rather than an Oregon bridge. Washington State has been tearing out historic bridges like they are some form of weed taking over a garden. Anyway, I found an interesting 1917 discussion of this bridge with photos: http://books.google.com/books?id=NdENAAAAYAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false