That's a grand design, and "lids" over the freeways are all the rage on Mercer Island and in Medina. I'm not convinced that a lid would reduce the Columbia River Bridge's wind resistance, especially if it has a lot of trees on top.
Secondly, The Columbia River Bridge is very long, and I don't know that Washington and Oregon could fund this. Washington already has several infrastructure improvement projects underway around Seattle, including the State Route 520 bridge expansion and State Route 99 tunnel project. A flyover-style overpass was just completed as part of the Interstate 5 - State Route 18 exchange rebuild, to make the interchange more safe.
Secondly, The Columbia River Bridge is very long, and I don't know that Washington and Oregon could fund this. Washington already has several infrastructure improvement projects underway around Seattle, including the State Route 520 bridge expansion and State Route 99 tunnel project. A flyover-style overpass was just completed as part of the Interstate 5 - State Route 18 exchange rebuild, to make the interchange more safe.