[Butch Cassidy Slept Here]

First, I'm assuming you're talking about travel within the USA.

Having a parent, or someone else acceptable to the airline, pay an "unaccompanied minor" fee to the airline is the easiest way to "legitimize" your travel. However, if your travel involves more than one airline, a fee must be paid, in advance, to EACH airline. Also, it's possible the "second" airline might, in addition to the payment of the fee, require a parent to be present when you check-in for your first flight with the "second" airline. Otherwise, I suspect if you're less than 15 years of age you probably should, at least, be carrying some documentation with you such as a notarized statement from, ideally, both parents or a legal guardian.

What an airline tells you on the phone is, almost, worthless. This board is full of stories of people being told one thing on the phone, then they get to the airport. The agent looks at them like they just landed from Mars! Getting the airline to quote you an age in an E-MAIL is more effective. Now you have something in writing. Make extra photocopies of that e-mail. Airline agents will, sometimes, tear-up something that is contrary to their (anti-customer)purpose.

For what it's worth the youngest age I can recall travelling "unaccompanied" at was 14. At the time, no fee was paid or anything not required of an adult was asked for. HOWEVER! That was 1963. Accordingly, with all the changes in regulations and laws since, it might as well have been two centuries ago!

Amtrak may be more leniant than the airlines as to unaccompanied travel by those under 18. However, if your trip involves only one train you may be on safe ground. Otherwise, if you're making a change of trains in Chicago, you will need to clarify what the laws in Illinois and Chicago say about unaccompanied travel. I once observed a young girl being taken into custody at the Washington, DC Greyhound terminal for no reason other than that she was a minor and travelling alone.

So, if you’ve found an airline that will give you hassle-free travel up to a certain point you might consider ground travel beyond the point you are able to travel by air. That is, of course, as long the law enforcement authorities at your “transfer” city don’t object as I’ve described above.

Whether it's the airlines, Amtrak, or the bus: If you're under age (a minor) it's very important to be nice to the airline staff and crew--no matter how obnoxiously they treat you. Your age could allow them to play the "minor travelling alone" card and have you taken into custody, again as described above. Likewise the same would apply to any form of ground travel--Amtrak or bus.