NYC train searches: Eighty-six year-old white grandmother? Search her. Twenty-two-year-old Arab man? Maybe not. It's random, both for sensitivity reasons and, we assume, the warped Fourteenth Amendment:
Kelly said that, in general, every 10th rider - or some other set interval - would be stopped before they hit the turnstiles and asked to open their bags or boxes for inspection. If illegal contraband is found in the process, riders will face arrest. If not, they'll be free to go.
Link.