If I were the mayor of Chicago, I'd take that money and spend it at the airport itself. This line shaves 25 minutes off the travel time for a fairly small subset of people. The gains to be made at the airport are far greater. I get there 25 minutes faster, only to spend the next hour screwing around at the airport. If we:

1. Staffed security such that there was never a line, 2. Staffed the ticket counter such that there was never a line, 3. Installed double ended jet bridges so that we could load and unload the plane twice as fast, 4. Put moving walkways everywhere, 5. Improved staffing and efficiency of baggage handling, such that you could drop your bag 20 minutes before the flight and have it get on the plane,

We could shave 30 minutes off the airport experience, for every user of the airport, not just the ones that happen to be coming from downtown.