ORD-B37-MDW: how the heck would they do it?

I've thrown this question in as a part of various transportation threads and never got a real answer. Perhaps it deserves a thread of its own. How in the heck can you set up an express rail system connecting O'Hare to Block 37 to Midway? Do you do it with existing blue and orange tracks? rail right-of-way? new construction? and if you have new construction, is it economically viable to just to create a downtown-airport express line? and is there land for rail expansion in the denser north/northwest sides of the city? Unlike the red line, where a number of north side sections have 2 sets of track, I can't think of anywhere on the blue line going from the Dearborn subway to O'Hare where there are more than one set of tracks. I believe that is also true on the Orange from the Loop el to Midway (although I'm not positive). ONE SET OF TRACKS: WHERE IN THE HELL DO EXPRESS TRAINS PASS LOCALS....DO THEY SWITCH TO THE TRACK IN THE OPPOSITE DIRECTION, RUNNING THE RISK OF A HEAD ON CRASH (EVEN WITH THE BEST OF CONTROLS?) And if other trackage is used, how can you justify the cost? Why is it that plans can be drawn up for this CTA super station between State and Dearborn, but the CTA isn't telling how in the world we're supposed to get to the airport? Meanwhile, if Metra were used rather than CTA, the only construction needed for a direct O'Hare link (I'll leave Midway off the tables on this one) would be to build subway tracks (to accommodate Metra, not CTA) from Metra's existing O'Hare Transfer station, under Manheim to the airport. Metra trackage is set up to operate as express on all lines. Metra would have a choice of either Ogilvie or Union Station for a downtown terminus....both these stations have west side lines that converge over Hubbard's Cave and connect to the existing O'Hare stop. And if the RTA really wanted to make this a reality, it could choose Ogilvie over Union Station and build a direct pedestrian link from the Green Line's Clinton's station directly into Ogilvie (something more stretched out, but akin to CTA's three subway/el stations: Clark/Lake, State/Lake, Roosevelt Rd). That's all it would take to get to O'Hare: • subway from O'Hare Transfer to O'Hare • Ped Link from Clinton CTA to Ogilvie I'm not familiar with Metra's southwest side trackage to know if a similiar situation could be used for Midway. Thoughts?>