Correction: An earlier version of this article incorrectly transcribed a word in the letter from Bobby Baum to Dr. Gridlock. He wrote a proposal for a new Metroline tunnel from Rosslyn to the Yellow line was “topologically” correct, not “topographically.” Also, the answer to that letter incorrectly referred to the proposed tunnel as going west from Georgetown to Thomas Circle. Thomas Circle is east of Georgetown. This version has been updated.


Dear Dr. Gridlock:

One point about the proposal for a new downtown Metrorail tunnel from Rosslyn to the Yellow Line has attracted little attention: It’s topologically correct, tying together the loose ends of the Silver and Yellow lines. This would greatly simplify and improve the efficiency of the system.

There would be only five rather than six lines (the Yellow Line running from Route 772 to Huntington), and the confusing Rush Plus rerouting could be eliminated.

One major disadvantage is that there would be no direct transfer between the Yellow and Green lines. Putting the new tunnel under Ninth Street rather than 10th would partially solve this problem but still leave a rather long walk between the lines.

Anyone have a simple solution?

Bobby Baum, Bethesda

DG: I hope this is just the first of many conversations about the long-range proposal that Metro is developing to guide the Washington region through the middle of the 21st century. It’s important, of course. But it’s also fun. The transit planners who presented their draft of the “Momentum” proposal last month included enough interesting proposals about new tunnels, stations, bus lines and transit connections to fuel many debates.

That’s pretty much what they are hoping for. But they don’t want it to end with just talk. They want a new generation of regional leaders, the successors to the generation who built the original Metro system, to step forward and convert talk into action.

Baum cites just one of the many fascinating proposals in the Momentum document, and it’s on the outside edge of the planners’ vision. Something that could be accomplished around the middle of the century, they suggest.

Before we get that far, said Shyam Kannan, Metro’s planning director, there are a few other projects that could greatly expand the transit system’s ability to move people. Among these goals for 2025 are all-eight-car trains. No more sixes.

They would help provide the extra train capacity that would get us through to the projects envisioned for the middle of the century.

Kannan is not thinking small. Creating a complete eight-car train system alone would cost about $2 billion. And that’s not the only big expense of the first round of investment. Kannan said we should also think about easing the current shortage of service for Blue Line riders at Rosslyn by building additional track connections or creating a second Rosslyn station that would separate the Blue Line from the Orange and Silver lines.

The additional track at Rosslyn could allow the Orange and Silver lines to connect directly with Pentagon and stations to the south. A second station would allow the Blue line to be separated from the Silver and Orange lines, freeing up more track space for additional Blue Line trains to reach Rosslyn — something that would make the current generation of commuters much happier.

They might all be retired by the time we make the next leap, to the stage that Baum talks about.

The plan for 2025 buys time and space. But we will run out of both eventually. The Rosslyn tunnel, the tunnels through the District and the bridge over the Potomac, can handle 26 trains per hour. And during peak periods today, that’s how many trains they carry.

By about 2040, the Metro plan estimates, we will need more tunnels so we can add more trains.

Among Metro’s proposals, the only line that wouldn’t benefit directly from new tunnels is the Red Line. The proposal Baum describes includes two tunnels, by Metro’s reckoning. One would create a new Potomac River crossing at Rosslyn, leading into Georgetown then traveling east along M Street to Thomas Circle, at 14th Street NW. In that area, it would link with another new tunnel along 10th Street NW/SW, which at its northern point would swing west to Thomas Circle.

That not only would put new stations in a ring around the old downtown stations, but would also allow the Green and Yellow lines to travel in separate tunnels, potentially increasing the number of trains.

Suggesting how early we are in the planning process, Metro’s map of these new tunnels marks them only with big, fat arrows. Baum goes beyond that by suggesting that the tunnels could accommodate a single-seat Yellow Line ride between Route 772 in Loudoun County, western terminus for Phase Two of the Dulles Metrorail, and Huntington, current terminus for the Yellow Line.

Most people wouldn’t want to go quite so far, and Baum has a good thought in wondering where a rider could make the transition to the Green Line in the District to reach an alternative destination.

We’re probably too early in the planning to talk about limiting the palette of Metro line colors. But I do think it’s likely that by the time some version of this plan is built, Rush Plus will exist only as a framed poster in a transit museum.

Like Baum, you might find something missing from the transit proposals you’ve seen so far. Or you might want to put in a good word for something that should become a top priority. Let me know.