Which will effectively shut down the economy of the city. Took me 2 hours to drive into town at rush hour yesterday, and I only went as far as Irving Park. Add 10k or 20k more cars to the mix and it will come to a stop. As to changing rail infrastructure, the CTA is teetering on the brink of collapse as it is.

The TSA method would be to put a few visible checkpoints at a couple of the biggest stops (Union Station) and leave the smaller stops untouched. So, the evil terrorists could just get on at another station, but Ma and Pa Kettle would see how hard the gov't is working to protect us at all costs.

Like everything else the TSA does, it will inconvience citizens and visitors, but the terrorists will just shrug their shoulders, smile, and work around the system. Nothing they do will actually stop a real trained attacker from finding an effective way to act. (OTOH, real old fashioned police work will stop them, but that is more difficult than Taking Shoes Away).