Metra accepts folding bikes on board at all times. However, during rush hours Metra conductors will likely request that the bike be bagged. Pretty much the same policy on the L. Bus drivers in Chicago can be a bit more nitpicky, especially when the bus is crowded. I recall being asked to unfold my bike and put it on the bus rack once. If you commute Amtrak north to Milwaukee or south to Champaign or Carbondale, be sure to bring a copy of the policy as there are still some rogue conductors that don't grok the concept of a folding bike.

Thanks for that Lalato. I'm just now back in De Kalb, but haven't yet unpacked the two crated machines I brought back from Taiwan as accompanied baggage. Incidentally, the smaller, lighter, and more high tech of the two (pix up next week at the latest!), was packed by the manufacturer unfolded in a fullsize bike carton, for which United Airlines (first quarter 2011 losses = US$219 million) charged me $200 to take aboard (three plane changes between Taipei and O'Hare); and I wasn't in much of a position to argue an hour before take-off. They did accept the smaller bike box containing the larger bike (65 cm or 26" wheels I think), which was packed folded as falling within the usual luggage allowance at no extra charge.