So here are some thoughts on the I-5 Columbia River bridge and route through Portland. If we are going to spend billions let's get something that will be useful out of it.
Create an elevated platform above it for high speed rail. The main thing holding this back is the already overloaded privately owned freight lines. Using the right of way we already have is the only way to get a fast system we can afford.
Keep existing freeway and bridge width, it will be more than enough for autonomous vehicles, the reason freeways are so wide is that humans are easily distracted and not that good at driving.
Make all bridge and freeway use metered, so use it you pay for it.
Increase the surface street and neighborhood connectivity with large overpasses with parks and housing on them.
The future is neither light nor dark, it's what we make it.