I agree with alexjon. If we care about the health of our cities, freeway removal is the way to go.
http://www.preservenet.com/freeways/
I grew up in Milwaukee, and the removal of the Park East freeway has been an incredible improvement for the area. Grade separated, limited access, high speed roadways have no place in the fabric of our cities.
Improve the I205 and rebrand it I5, and come up with a 50 year plan to remove all other freeways from Portland. That would be incredibly forward thinking and serve as a model for other cities.