This wall-like structure in the median of the Dulles Greenway is preparation for a future bridge over the toll road. (John Kelly/The Washington Post)

Construction workers have built a large wall in the median of the Dulles Greenway, near the exit for the Loudoun County Parkway. It looks about 15 feet high and maybe 20 feet long. I assume it will have to come down when they extend the Metro in a couple of years. Do you have any idea what purpose it has now?

Bill Buermeyer,


Dulles Greenway chief executive Tom Sines told Answer Man that a number of people have expressed concern and curiosity over this concrete . . . thing.

A street sign that has “UNIT” displayed, denoting the first block of a D.C. street, with addresses between 1 and 99. (John Kelly/The Washington Post)

Is it a billboard? some wonder.

Is it a screen for showing drive-in movies?

Sometimes Tom jokingly tells people it is the Greenway handball court.

It is, of course, none of those things. It isn’t even a wall at all. It does not separate. In fact, it will help join. It is a pier for a bridge that has yet to be built.

The bridge will carry Barrister Street over the toll road. It’s one of several improvements to develop areas adjoining the Greenway. Because Metro’s Silver Line will eventually go down the middle of the Greenway, it was decided to put this particular bridge pier in first and build the Metro rails around it, rather than vice-versa.

“We are obligated through a contract from way back in 1993, when the [Greenway] deal was put together, to build that bridge once roads are complete on either side of the Greenway,” Tom said.

“We don’t know when that will be. It’s largely dependant on growth brought by Metro. Trying to put that bridge pier in the center of a Metro track would have been virtually impossible. Anything we’re going to be building in the median, we need to get in place before Metro does.”

Tom said the closest Silver Line Metro stop will probably be what’s currently known as the Route 772 station.

As for the Greenway, it opened in 1995 as a way to speed motorists through Loudoun without having to sit in traffic on Route 7. Funded by an ownership group that included wealthy Middleburg resident Maggie Bryant and her son, Michael Crane, it was the first privately owned toll road built in the United States in nearly 200 years.

The original agreement called for it to be turned over to state control after 40 years. An additional 20 years has since been tacked on.

At first, tolls on the 14-mile road were $1, but that soon proved not to be enough. The cost to motorists has risen since then. The maximum toll during peak congestion times is $4.90.

Although we’ve lived in suburban Maryland and driven up and down North Capitol Street for almost 17 years, we just noticed something on the street signs along all the cross streets: They have the word “UNIT” below the sign. What does that word indicate?

Amy Schmidt Stowe,

Silver Spring

Let us explain it this way: A city block is enumerated by the range of the addresses on it. The White House, with an address of 1600 Pennsylvania Ave. NW, is in the 1600 block of Pennsylvania. Ford’s Theatre is in the 500 block of 10th Street NW — at 511 10th St. NW, to be exact.

If you look at a corner street sign in the District, you’ll see it includes a numerical reminder of which block you’re on: 500, 1600, whatever.

Washington is divided into quadrants, with addresses rising the farther you get from the quadrants’ dividing lines: North Capitol, South Capitol and East Capitol streets, and the Mall.

But what do you do about that first block? Do you call it the “zero” block? No. That first block — with addresses between 1 and 99 — is known as the “unit” block. Posting the word on street signs reminds motorists and pedestrians of where they are.

This reminds Answer Man of one of the best impromptu one-liners he ever delivered. It involved the unfortunate John Wayne Bobbitt and the location where his manhood was retrieved. Fill in the rest for yourself.

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