PUT YOURSELF in the position of the traveler who comes up the escalator at the National Airport Metro Station looking for a train. But which train? The signs seem to imply that the newly opened Yellow Line is using the track to the left, and the familiar Blue Line is on the right. But soon it begins to dawn on you that trains on either line can leave from either track. Perhaps you are a visitor to Washington who has been told to take the Orange Line. There seem to be no signs for the Orange Line at all.

The reason is, of course, that for imperative reasons of great complexity the Blue Line outbound is the Orange Line inbound. So don't worry about the Blue Line signs; the train isn't going there anyway.

And here's a train, ready to go. Is it Orange, Blue or Yellow? That's very hard to tell. Metro prides itself on its highly automated system, which means that there's no one to ask. In a perfect world you could tell from the mechanical signs on each car, but unfortunately those signs don't work.

It is, in fact, the Mystery Train. Since there is no way of knowing where the Mystery Train intends to go, your best bet is to climb aboard and see what happens. After the train is moving, the pilot will tell you over the public address system which line you're on.

Many people will find that riding the Mystery Train introduces a welcome note of adventure into their overregulated lives. But there are other people who are in a hurry. They do not seek further Metro mysteries, and want to know where they are headed. To judge from the comments one hears at the station, they seem to be the large majority. For those people, Metro might usefully put someone in uniform on the platform to provide answers.

It is probably unreasonable to expect a new subway line to open without a certain amount of confusion. The trains are running well, for which Metro deserves congratulations; it's an intricate operation. The troubles with the signs are a relatively minor matter, and hardly grounds for great complaint. But it remains true that, as a general rule, people would kind of like to know where they are going.