There is a very strange overpass on the Clara Barton Parkway near Glen Echo. As the parkway sweeps to the right at the MacArthur Boulevard exit, it passes under some sort of bridge. Was that bridge part of a grander plan for the interchange, which was abandoned? Or is it left over from some earlier roadworks which weren’t completely removed?

Buck Shinkman, Bethesda

Answer Man recently embarked on an expedition to find the famed Bridge to Nowhere, as those in the National Park Service call this vestigial bit of highway. He parked on MacArthur Boulevard, braved traffic and scampered up and down embankments to reach the decrepit bridge. Its design — concrete, with triple-tiered guardrails — matches that of the George Washington Memorial Parkway on the other side of the Potomac.

That’s because the bridge was part of the GW Parkway, or was meant to be.

In 1930, Congress approved the construction of a scenic parkway on both sides of the river. The eventual design called for two lanes in each direction, going from Great Falls and ending at Mount Vernon in Virginia and Fort Washington in Maryland.

Virginia’s parkway was built first, though its northern terminus is the Capital Beltway. Things were spottier in Maryland. The Park Service bought land piecemeal, expecting to eventually link all the bits. Securing the right of way in Prince George’s County was especially difficult. Landowners and environmentalists complained, and so did some politicians, who pointed out there was no need for a riverfront parkway from the District to Fort Washington.

The Park Service did build the parkway north to Glen Echo and beyond. But it’s only two lanes in some places.

“They built the overpass bridge there in anticipation that they would accrue the other lands they needed to complete the parkway inbound,” said Matt Virta, cultural resource manager for the George Washington Parkway.

They built other things, too. South of the bridge, back in the woods, are five-foot-high concrete columns topped by manholes. “They would have been at pavement level, had the other roadway been built,” Matt said.

By 1969, it was clear that the Maryland parkway would never be completed. And now it’s just too much trouble to tear down the Bridge to Nowhere.

“It’s one of those little quirks of history,” Matt said.

In 1989, the Maryland side of the parkway was named in honor of Clara Barton, founder of the American Red Cross.

From Sept. 3, 2006

In Metro cars, you will sometimes notice in the driver’s compartment a placard that fits into a slot in the front of the car with the line’s color printed on it, i.e., “RED.” Today I saw a placard with the word “WHITE” printed on it. Do trains ever assume the color white?

John O’Hanlon, Germantown

No. You’ve seen a Metro map. You know there’s no White Line. So what’s up?

Those plastic placards — about the size of an LP (you remember LPs, don’t you?) — are used to indicate the color of the line the train is traveling. They slide into a slot at the front of the driver’s compartment in older trains so riders standing on the platform can see them.

Our Metro system may have five lines, but there are only three cards. One is blue on one side and orange on the other. One is red on one side and yellow on the other. And one is green on one side and white on the other.

The white side should never be placed facing out from the front of the train. If you’ve seen that, the driver has made a mistake. But you may see the white card on the driver’s door, facing the passenger compartment. One train operator told Answer Man that drivers sometimes prop a card up there to keep riders from peering in.

All this colorful language prompts a question: Why are Washington’s subway lines named after colors? Other cities have different nomenclature. The lines on London’s Underground come from all sorts of places, including the names of the original private companies that ran them in the 19th century (Metropolitan Line) and portmanteau words based on the stations served (the Bakerloo Line’s stops include Baker Street and Waterloo).

Other cities use the names of the stations at the end of each line. That method was seriously considered for our Metro.

“If you look at early planning documents, what was proposed was to name them after their destinations,” said Zachary M. Schrag, an assistant professor of history at George Mason University and author of “The Great Society Subway.” “People are talking about a ‘Rockville Line’ or a ‘Vienna Line’ or a ‘Silver Spring Line.’ ”

The District had a problem with that, because all the lines would be named after places in the suburbs. So colors it was.