Expressway removals

[Markster]

That's a cute idea, but what happens to all the displaced traffic and passenger trips?

Well, in the majority of those cases in that article (Portland, Rio Madrid, Seattle), they built (or are building) a replacement freeway nearby. Or underneath. Not exactly a removal, simply a relocation, which comes with the costs associated.
Two others (San Francisco, Milwaukee) have removed freeway stubs, which don't offer altogether that much for the transportation network. In SF's case, they added the F streetcar, which replaces the people-moving capacity.
And the final one, Dallas, is certainly counting their chickens before they're hatched.