No, this is not the clunky title of a new Dan Brown thriller or the name of some amazing magic trick we've been working on in our spare time, because we don't really have a lot of that. And while we might know a thing or two about secret Masonic hand-shakes, we have, alas, been sworn to eternal secrecy.

Instead we'll simply expand a bit on our previous article about code-sharing, that ever more popular, creative, arguably deceptive and definitely confusing—some might say bizarre—practice of not just selling the very same airplane seat in variously branded guises and sometimes at widely (and wildly) diverging prices, but mixing different modes of transportation in one single fare and marketing them all as air travel. So hop on, fasten your seat-belt and get ready to descend into the twilight zone of travel lore.

Code-share agreements combining air and rail travel are not a new phenomenon, but they are becoming increasingly common wherever fast train service to nearby cities makes connections from major airports with a convenient train station more efficient than flying overloaded puddle jumpers. It certainly brings the whole hub-and-spoke metaphor down to earth again and back to its more literal definition involving wheels and rods rather than wings and interminable transfers.

These arrangements are especially prevalent in Europe between national airlines and national railroads, such as Lufthansa and Deutsche Bahn, and Air France and SNCF, and even found stateside on a smaller scale, where Continental sells seats on Amtrak from Newark to Philadelphia, Wilmington and other East Coast cities.

We recently chanced upon a new twist on this evolving theme that is noteworthy not just for the partners involved—a U.S. airline, United, and a foreign national railway, France's SNCF—but also the distance covered by ground transportation, about 500 miles.

In this particular instance, you're supposed to change planes at Paris Charles de Gaulle Airport, but when you hear the call to board United Airlines flight 9764 bound for Marseilles, do not, we repeat, do not proceed to the gate, but try instead to find your way to the nearest railway platform because you'll actually be parking your rear end on a high-speed double-decker TGV train that will hurtle the whole of your being down the tracks to the Mediterranean coast in little over 3 hours, almost as fast as a Boeing 737.

(You can see a sample itinerary on our Fare of the Day page. Incidentally, a feat like this is feasible in few countries other than France, thanks to its remarkable high-speed rail network which just this spring set a new world speed record for conventional trains at 357 mph.)

So what's next? Will it be long before some smart airline executive decides to team up with U-Haul to sell you on the no doubt much ballyhooed "freedom and luxury of independent travel" along with a "generous baggage allowance" and an iron-clad guarantee "to get you there on your own time" when they can't get their planes off the ground?

And what's to stop Podunk Paradise Airways from simply slapping their sign on a donkey, hitching up the wagon for your luggage and sending you quietly ambling down the gravelly path to nowhere?

Who knows, some day you might even be able to market your Monday morning car pool to as Moe's Expressed Air and turn an extra buck by offering cramped seats, surly service, bad coffee, bumpy rides, endless delays and throwing some worthless bonus frequent-flier miles at hapless fellow commuters. Just don't tell anyone where you got the idea...

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