You know, I just going to say this.....t's easy to look at a map and say these two railroad stations should be linked by tunnel. What's not easy is getting the people in the right-of-way on board with the project without any major lawsuits (and because this is the USA there WILL be lawsuits from at least ONE person along the route who fails to understand the importance of said project and put their "rights" first), trying buy up property within the City of Chicago which is expensive, and properly digging the tunnel without disrupting too much. Since what you're asking is connecting two semi-elevated train terminals with a tunnel, that tunnel can't be built quiet with a TBM. It going to need to be dug up the old fashioned "Cut-N-Cover" way which means hollowing out streets to build said tunnel. Not to mention, you can do all of that and still have some sort of money woe come and stop the project in it's tracks. Think Block 37 and The 2nd Ave Subway. This is why there so many disconnected train terminal around the country. I remember hearing about the crap SEPTA had to go through to connect their two railway terminals in Philadelphia. The project started in 1963! It wasn't until November 84 when it opened and what we got was half-assed to say the least because of so many money woes and protests from Chinatown.

Or they could just make Union station have more than 1 through tracks. Also as much as us railfans/urbanists like to promote through running stations/tunnels, they are not often the best investment. While they can add some more one seat rides, they don’t solve bigger issues like frequency and sometimes worse reliability.

Neither of those really make sense in practice. OTC and CUS are so close that it would be easier and probably more efficient to just use the through running capability of CUS (The easternmost tracks and mail platforms). A crosstown tunnel from the CNW freight spur that used to serve Blommer Chocolate and the Tribune, north of OTC, with connections to Millennium and CUS would enable frequent through running. And the St. Charles Air Line connection would enable running from CUS onto the Rock Island tracks.

"crayons on a map" isn't really helpful here

If you’re going to ask for rapid transit on the West Bank of the South Branch of the Chicago River to Serve Chicago Union Station and OTC, they should dig a Blue Line Clinton Street Subway down from Milwaukee Ave. South to Congress/Ida B. Wells Pkwy to make a Blue Line Loop so trains can either be “UIC Halstead Via Clinton St” or “Forest Park Via Dearborn St”

The Red Line prior to the Belmont flyover ran every two minutes. The CTA said that the Belmont flyover will add 6-9 tph on the Red Line, so it is reasonable to assume the whole of the State St Subway can handle 36-39 tph. Even so, I started out with 30, and gave 20 to the Red Line and 10 to the Purple. If demand changes, we can change this split. I also designed the Clark Interlocking so that the Brown Line won't have any merges until the Loop, which means the Brown Line can absorb that extra capacity. The Brown Line is on the outer Loop tracks, where there is extra capacity to be spared, which means this won't be an issue. The only issue that I see is that the CTA has to buy more trains and expand the Racine Yard, which is doable. Hope this answers your concerns!

​@@techtransitassociation Why not making an Entirely new line to serve it similar to the Pink Line which was created from a former Blue Line Branch.

Stub status will change as Woodlawn is "Re- Developed".

The Yellow Line Platforms cannot hold more than 2-4 Train Cars

The politicians are car-brained to extend to the O-Block Park.

Money for more trains and expanding the Racine Yard.