I don't live in Seattle so maybe I don't read the gov reports the same way, but the link looks to me like it's a finding by the DOT that there is no adverse impact from the plan and therefore no need to do a full environmental impact study. I don't see anything in the linked page or the determination .pdf about not following the plan or anything like that, just that it won't be bad for the environment, which I would expect. If I'm missing something, sorry.