TSA does not enforce this policy. The airlines do.

Is that better? Does that clear up the confusion?

Bart
I don't know about that. They do occasionally. I had some untrained TSA folks claim my computer bag was a carry on.

The good news is that my airline of choice never enforces it against me. I often find a fellow traveler willing to hold my third carryon for the moment or two while we pass the moat dragon. Then, safely within the checkpoint, I thank the fellow traveler and reclaim my third carryon.

<sigh> Well, all I can say is that the TSA SOP specifically says it is none of our business how many carry-ons you take with you. It is not our job to enforce the 1 + 1 rule.

Actually the 1 + 1 rule is ambiguous in its origins. I believe that it comes from the AOSSP. This is alluded to in FAA regulations and is incumbent on the aircarriers to submit one of their own or adopt a model one. I think that is where the 1 + 1 rule comes from. So it could be said that it is airline policy. I wrote the FAA to ask about it and they never wrote me back. :(

Here's a couple of posts explaining the origins of the one plus one rule:

http://www.flyertalk.com/forum/showthread.php?p=2688840 (post #6)

http://www.flyertalk.com/forum/showthread.php?p=3379916 (post #3, correcting you on this same error)

For nearly a year after this FAA (now TSA) rule was implemented, AA's written policies invited F pax to carryon up to three carryons. Its policies are now in conformance with the government-imposed rule, but nobody at the airline seems to care how many carryons I have.