My dream is to dig a trench from say 290E to Ben White. Bottom of the trench is northbound. Cap it then have southbound on the next level. Cap that and have surface blvd/frontage/rail.
If the frontage lanes could be built atop the highway lanes, that widens the possible footprint. We could probably get 7 lanes each direction even in the narrowest spots. Each level would have to have shoulders and a safety lane. Would also need exit/entrance ramps. I'll leave that to the engineers.
If we really wanted to go all out, you could have subway inside the trench as well, on either side of the roadways.
Anybody have a trillion dollars?