The writeup above is pretty good. There are just a few things to clear up.
- The above list is a complete list of Portland Willamette River bridges carrying auto traffic. There is a railroad bridge located between the Fremont Bridge and the St. Johns Bridge.
- 3 bridges cross the Columbia River into Vancouver, Washington. From east to west (downriver), The Glenn Jackson Bridge, the Interstate Bridge, and another railroad bridge. The auto bridges carry Interstate 205 and Interstate 5, respectively. Unlike the Willamette freeway bridges (the Marquam Bridge and Fremont Bridge), pedestrians and bicyclists may cross either span.
- The Ross Island Bridge is a fixed span.
- Ridiculous to compare? Not necessarily. The St. Johns Bridge is the 57th longest suspension bridge in the world, behind the Golden Gate Bridge at #5 and Bay Bridge at #21. However at the time it was built in 1931, the St. Johns was #9, behind a gaggle of New York Bridges, with the Bay Area Bridges yet to have been built. And of course, something could be said for the eclectic collection of bridges in a relatively short section of river.
Suspension Bridge info from http://www.civeng.rutgers.edu/asce/suspension.html