Drawbacks, Problems and other Considerations
First drawback for this plan is the sheer amount of money it's bound to cost. From adusting the rails (and adding in third rails) so that the CTA El vehicles would be able to make it down rail lines made for Metra Superliner vehiclies to the rebuilding of a number of stops to make them ADA compliant (among other laws), the cost would be high, maybe prohibative. Even the mere extension of the Green Line down the South Chicago Branch would include the following charges:
- adjusting rails, including third rail
- removal of cantinary for entire length
- placing overpasses in places where road traffic is heavy (Stoney Island is one that comes to mind)
- connecting Green Line with the South Shore Branch
- a Transfer station between the Green line and the Metra Electric
- dealing with the now-useless connection between the Main Line and the South Chicago Branch
- dealing with the two present southern endpoints of the Green Line
And, of course, there's the problem of whether Metra would give up the South Chicago branch, and for how much.
All this, in an era where the keyword is not so much expansion but maximization. You have a system who plans a route based not so much on usability or expansion of service but instead on using what they have. Ergo, the Circle Line, an idea feasible only because of the maximum punch for the minimum amount of money or disturbance.
Second Drawback: Everything I've proposed is on land owned by Metra. Right now, there is precious little cooperation between Metra and the CTA, and I doubt that Metra would want to give up land and responsibility to another. Shared responsibility (Main Line, part of the Red Line extension) would be another can of worms entierely.
Third Drawback: What to do with the two southern ends of the Green Line? It may be possible to extend to the South Chicago branch via 63rd, either via a quick turnoff or directly to the Electric Mainline and down the present access. Whatever way you do the connection presents problems (down 63rd would bring down the wrath of churches and other groups grousing over "the darkness an EL line would bring;" other connections have thier problems.).
The west branch is another problem. Do we do another "stub line" like the lines which had dotted the El line for years? Many of them drained the systems for years, others worked only to be abandoned by the customers in the end. No matter what, the stub lines ended being a drain and a curse on the Chicago system of Els, and their disappearance (outside of the Skokie Swift, built as an express line for commuters) has pretty much been unmourned except by railfans. While it would be nice to extend it, the question remains: where to? And why? Plus you can't tear it down, the CTA would have to repay the Federal Government millions of dollars of money if they were to tear down that stretch of rail.
I could easily see a combination of the first phase of my plan combined with an activation of the Gray Line, concept down the mainline and the Blue Island branch. The transfer station would allow for movement from the Electric to the Green Line and the rest of the El System, and while the South Chicago line would be costly the rest of the service could be implemented as cheaply as possible.
It's also probably the best I can hope for, increasing service to the south so that the South Shore System will have space at "Millenium" station.