I was reading a slashdot story when I happened upon this post claiming that the U.S. Government is tracking cars using embedded RFID chips in tires. I recalled reading something about it awhile ago, but only thought it was for border crossings (Canada/Mexico). From this post it seems they want to track you when you drive on the Interstate, under overpasses, and across state/boundary borders.
Of course, this will never be abused comrade. May I see your papers?