Originally Posted by
MKE-MR
You could but it would be a long walk along a highway

. Have you ever been to ORD? Terminal 5 is not connected to the other terminals. You'd need to allow at least 60-90 minutes to exit terminal 3, take the train, re-clear security in terminal 5.
I think a "friendly" CPD Officer will have pulled over to stop anyone from doing that.