Oh man. No lie... this is the intersection I redesign in my head to fall asleep. Maddening! Really glad you guys are noodling it as well. The TKC Rotary must have shown up in the analog version of 'Crazy Highway Ideas' in 1947 --- and somebody said "Sure! You look like a smart feller. Why not?"
Gotta say, I'm kinda liking elements of the two rotary idea, too, but here's what I'd throw in.
Reconsider: There is no reason to keep a lot of what is here - all built before 93 went in so it's
extremely overbuilt. Mega carchitecture to handle vastly more cars than actually use it. Throughput targets need to get cut.
Simplfy: In general there's no reason for expensive over-underpasses if you put the whole area on a strict road diet. If fewer streets come in to the TKC rotary unnecessarily, fewer roads need to get built. Less is more. Slow it down uniformly, smooth it all out. Big picture.
Columbia Road/93: There is room for
a tight SPUI - which would eliminate a light or two and make the whole area work better, reducing conflict traffic between there and the rotary.
Day Blvd: Should be knocked down to 2 lanes and removed from the rotary altogether. Day Blvd should move (north to south) from the beach to around the waterside of the old Bayside Expo/Teachers Lot, to join Mt Vernon by Gibson Health. It's a local road, not a friggin' highway. We should treat it that way. Bikes, walkers, quiet, safe. As a set up on the north approach, rework the intersection between Day Blvd at Covington and G.
Columbia/Old Colony on West: Reroute all through traffic to Columbia/Old Colony on West side of Park. There is only a need for one 93 alternate 4-6 lane highway (which is how suburbanites, the main audience, uses it).
Mt Vernon will takes more traffic.
Feeders: Move the rotary adjacent feeders out from close proximity. All the pre-ramping within the 1000' approach is what causes the lion's share of the delay.
I will attempt to sketch this out.
The new TKC Rotary itself: By effective traffic smoothing on approaches, adding labeled slip lanes, reducing roads in and around, the fewer options will pull it all together.