What's with the gates?

[berkelman]

Over the past year or so, gates have been installed on several ramps (Fullerton, Webster, North) onto the Kennedy. I've never seen them down, but why were they installed?

[Mr Downtown]

One theory is that it's for presidential motorcades from O'Hare. More probably, it was in the works for several years as a Fatherland Security project, for contraflow evacuations from dirty bombs, etc.