WMATA's 50th anniversary from the start of service, Part 2b | Lessons learned: Proposed expansions and the Metrorail system we don't have

This is part of a series:

-- "WMATA's 50th anniversary from the start of service, Part 2a | The Original Approved Metrorail System (1968-1970)"
-- "WMATA's 50th anniversary from the start of service, Part 2b | Lessons learned: The Metrorail system we don't have"
-- "WMATA's 50th anniversary from the start of service, Part 3 | Stations"
-- WMATA's 50th anniversary from the start of service, Part 4 | Buses"

Each discusses what I think of as the lessons that should be learned from Metrorail, as a transit service and as an economic development augur.

Recently I acquired a copy of the February 1976 issue of "Metro Notes", a tabloid published by WMATA throughout the construction process.  The Approved Plan Map shows the current system, with 11 potential extensions.  Three were constructed:  (1) two Blue Line, stations from Addison Road to Largo; (2) from Rockville to Shady Grove on the Red Line; and (3) the Silver Line.  All were covered on the Approved Plan Map (1968-1970).  

Two infill stations were later added, NoMA on the Red Line ("Having Turned a Corner, Washington’s NoMa Is Coming Alive," New York Times) and Potomac Yards on the Blue/Yellow Line ("Metro's New Potomac Yard-VT Station Is Open. Here's What to Know," NBC).  

Because of the number of images, the map alone is a separate entry.  Note that I am sure to have missed some officially sanctioned proposals of some sort or another.

Where we are today:

Today's Metrorail system

6 lines, 130 miles of track, 98 stations.  No current planning for extensions or intensifications. Daily ridership was about 750,000 before covid.  The system exceeded one million riders for the Obama Inauguration, and had a number of peak days greater than 750,000.  

Today's ridership is about 2/3rds of peak.

The Purple Line Light Rail Link (opening 2028)

The Purple Line is a light rail link between Bethesda and New Carrollton Metrorail Stations in Montgomery and Prince George's County Maryland, and will also connect to the Green Line in College Park/  It will also connect to all three MARC commuter rail lines, at Silver Spring (Brunswick Line), College Park (Camden Line) and New Carrollton (Penn Line).

There will be 17 new stations in addition to the existing transfer stations.

The line was conceptualized in 1987, when Maryland bought rail right of way "abandoned" by CSX because it was no longer needed to serve the since shuttered electricity generation plant in Georgetown. 

The Purple Line is being constructed by Maryland.  

Like how the Silver Line was constructed by the State of Virginia and then given to Metrorail, Maryland intended to transfer the Light Rail line to WMATA too--which is different technology from the heavy rail system--but WMATA said no.  

It is still expected that service schedules, fares and mapping will be integrated with WMATA, at least this was intended according to a letter from John Porcari, then State Transportation Secretary, to Chevy Chase, Maryland c. 2015.

While the Purple Line was conceptualized as a fully circumferential line connecting all the legs of the Metrorail system (see below), only the section between Bethesda and New Carrollton is under construction.  No planning for extensions is underway.

The Metrorail system we don't have

If you don't plan for extensions or intensifications, you don't get them.  In the first entry, under transit infrastructure lessons, point 1:

While the early system was expensive and seemed extensive, it missed areas that would have been good to have been included, and WMATA didn't continue to work for expansion beyond the original system program.  

WMATA kept saying, not until we finish the original Approved Plan.  This meant that original concepts of extensions mostly did not come about. (I pointed this out to the first Dr. Gridlock columnist for the Washington Post, c. 1990.)

As the Purple Line light rail program proves, it takes decades to build rail.  If you do it in fits and starts it takes a lifetime.

To further explore this point, at the outset of construction of the system, there was an Adopted Approved Plan for the system, eventually slightly modified to have 103 miles of track with 83 stations, and separately, a set of recommended extensions.  Of the 11 proposed extensions, only three were completed. 

THE MAP: should pop up in a separate window

The expansive Metrorail system planned at the outset

Washington Regional Rapid Rail Transit System Map

Adopted March 1968. Revised February 1969 and June 1970

The map of the system, printed in that issue, and just before the system started operation, shows a number of "authorized" or planned "further" extensions.  These were the authorized extensions, listed clockwise from the map:

• Green Line, north from Greenbelt to Laurel, ≅8 miles
• Orange Line east leg, from New Carrollton to Bowie, ≅9 miles
• Blue Line from Addison Road to Largo (two stations
• Green Line, south from Branch Avenue to Brandywine, ≅12 miles
• Yellow Line south leg, from Huntington to Fairfield -- unknown.  I don't know where this is.  Commonly Fairfield in Fairfax County is thought to be west of Vienna Metrorail Station in the Fair Oaks area, not the Rte. 1 Corridor
• Blue Line west leg from Franconia-Springfield to Burke, ≅8 miles
• Columbia Pike Line from the Pentagon to Lincolnia 
• Orange Line west leg, from Vienna to Centreville, ≅10 miles
• What is now called the Silver Line, which was constructed in two segments, serving Fairfax and Loudoun Counties with 11 stations and 23.5 miles of track 
• Red Line one station extension  from Rockville to Shady Grove
• Red Line west leg, from Shady Grove to Germantown, ≅9 miles

If you ever wondered why Southern Towers in Alexandria is so tall, it's not just because of proximity to freeways, but also because they expected the Columbia Pike Metrorail Line to be constructed.

Remember, at the time of the initial planning, passenger railroad services were on the decline, so Metrorail is a mixture of a heavy rail subway in the core and a "commuter railroad" outside the core.

Since then, researchers have found that stations in the core of the region have the best ridership.  

A good example of this for WMATA is the Silver Line, it extends 23.5 miles further out into the suburbs, with 11 stations, but only has a daily ridership of about 36,000, while the Red Line, which is more focused on the core, but still suburban, had at least 136,000 daily riders.  Data source.

Interestingly, the very first plan for a Silver Line c. 1971, forecasted around 30,000 riders, so you could say the Silver Line is meeting expectations.  But the other lines have double or more the ridership.  Without Dulles as a destination, the line is less justifiable.

Most of the proposed extensions are exurban, but could be justifiable, IF AND ONLY IF, comparable to Arlington, those jurisdictions developed land use intensification plans in association with the expansion.  (Although this could be further criticized as sprawl.)

The c. 1991? WMATA Metrorail "21st Century" Map

I know nothing about the origin, but this was displayed in the office of then DC Councilmember Jack Evans, who served on the WMATA Board of Directors for many years.  Since it includes a circumferential Purple Line, which was first proposed in 1987, it was produced some time after 1987.

It shows:

• A one station extension to Gaithersburg on the west leg of the Red Line (not to Germantown)
• An extension to Olney from Glenmont on the east leg of the Red Line
• A Wheaton-Georgetown-Manassas Line serving Columbia Pike, with 12 stations, including one for Kennedy Center
• a Red Line east leg extension to Olney
• What became the Silver Line but  showing only three stations, but as far out as Leesburg, which is 17 miles further from Dulles Airport, and 11 miles from the current end of line Ashburn Station
• A heavy rail Purple Line, a circle line connecting the legs.  This line doesn't show many stations between the legs.  It does show Montgomery Mall, Tysons Corner, a connection at "Ravenswood" to the Wheaton-Manassas Line, National Harbor, and Andrews Air Force Base
• the Green Line south extension to Brandywine
• an Orange Line extension to Annapolis
• the Potomac Yards infill station in Alexandria
• and the Green Line being extended from Greenbelt to Baltimore, a distance of about 29 miles

Most of the proposed extensions are exurban, but could be justifiable, IF AND ONLY IF, comparable to Arlington, those jurisdictions developed land use intensification plans in association with the expansion.  (Although this could be further criticized as sprawl.)  Penn Line MARC railroad service to Baltimore means a Green Line extension there isn't warranted, as it's an unnecessary duplication.

Regional Transit System Plan, 1999

The graphic is referenced in this document.  The extensions were supposed to be operational by 2025.  

It shows (1) An extension to Centreville; (2) a loop for Tysons Corner; (3) an outer circumferential route (the Purple Line, but heavy rail?), from the Orange Line south of Tysons to Greenbelt; (4) an inner circumferential route (the Purple Line, but heavy rail?), from Bethesda to New Carrollton; (5) a line from Wesley Heights/Georgetown to Fort Lincoln; (6) from Columbia Heights? to Minnesota Avenue; (8) a separated Yellow Line to Silver Spring; (9) A line from Bailey's Crossroad-Columbia Pike to the Pentagon to Charles County, in part being a southern outer circumferential route (Purple Line, but heavy rail), and (10) extension to Fort Belvoir/Lorton.

It also includes the already approved extension to Largo then under construction, the previously referenced infill station at Potomac Yard, but for the first time, the New York Avenue Station (now called NoMA), between Union Station and Rhode Island Station, which began construction a couple years later.

Assignation of responsibility for expansion planning to the jurisdictions, not WMATA, 2000 

Silver Line, c. 2000

There have been many different planning iterations for a Silver Line, dating from the time of the initial Approved Plan(s) in 1968-1970.  In 2000, decisive planning was put into place by the State of Virginia, primarily to provide a Metrorail connection to Dulles Airport.   The final plan was approved in 2004. 

This Washington Post graphic is from 2007.  The first phase opened in 2014 and the second in 2022.

Separated Blue Line, c. 2000-2001

(Or a Separated Silver Line)

The original proposal for a separated Blue Line dates to 2001 ("If DC had visionary elected officials and planners it could use the new WMATA "BOS" study to push through the development of a separated Silver Line in DC (and Northern Virginia)").  The main purposes were twofold: (1) to provide a separate platform at Rosslyn, taking pressure off the Blue and Orange Lines; and (2) to provide a parallel line to the Downtown stations as a "relief line," presuming that as the system approached 1,000,000 daily riders, existing stations would be at overcapacity.  

Two secondary purposes were providing service to Georgetown and to provide an additional connection to Union Station, to support plans for expansion of the station and an expected doubling or more of railroad passenger train ridership.

WMATA dropped this plan, in response to a regional economic downturn.  It's the foundation of my concept for a more ambitious Separated Silver Line.

With post-covid decline of Downtown DC as a regional employment center, there is less need for a "relief line" for the Downtown stations.  But Georgetown "needs" a station, and to accommodate planned future growth for Union Station ("Union Station in Washington Has a Grand Development Plan," New York Times), another Metrorail connection would be advantageous.

Until the BLOOP planning, only the Arlington County Master Transportation Plan kept the Separated Blue Line concept alive in their planning documents.

Except for the section east, starting at Minnesota Avenue to New Carrollton, the line would no longer interline in Virginia and most of DC, which is an advantage for reliability.

Separated Silver Line.  My concept riffs on the separated concept, based in part by comments on a post at GGW.  Instead of separating the Silver Line at Rosslyn, it drops down from East Falls Church, sending it southward to Seven Corners and east along Arlington Boulevard, to Rosslyn and then across the river to Georgetown and then east of the existing subway lines, to Union Station, and from there to H Street as in the original plan and then connecting to the Blue Line again at Stadium-Armory.  

At the very least it would be better to connect to the Orange Line at Minnesota Avenue, adding one or two stations on the RFK Campus and Benning Road.  This would serve the forthcoming RFK campus, not just for the stadium, but also for redevelopment of the parking lots.  Perhaps a leg could go up up Bladensburg Road into Prince George's County.  It would also provide a Metrorail connection to New York Avenue.  

Regional Transit System Plan, 2010

From the document:

Assuming at least 10 years to construct major core capacity projects, we must identify a preferred expansion strategy and begin to preferred expansion strategy and begin to secure funding in the next 5 years

Regional Transit System Plan, 2013

This planing document fed into the next.  But it called for a lot more extensions, like the 1999 Plan.  I'm taking some liberties with this list.  Few of the examined opportunities made it into the Momentum Plan (next).  For rail it states:

(1) Purple Line in Maryland's portion of the Constrained Long Range Plan.  

And for WMATA by 2025:

(2) Metro Center/Gallery Place Pedestrian Walkway (this dates to 2002)

(3) Farragut North/Farragut West Pedestrian Walkway

(4) Second Rosslyn Station and Blue or Silver Line separation options

(5) Possible separation of the Yellow and Green Lines

(6) A potential Brown line loop from Friendship Heights on the west to Cherry Hill in Montgomery County on the east.

(7) The Beltway Line, circumferential, more north than the Purple Line

(8) End of Line Extensions: (a) Green Line to BWI; (b) Orange or Blue Line to Bowie; (c) Blue Line to Potomac Mills; (d) Orange Line to Centreville or even further to Gainesville; (e) Red Line to Metropolitan Grove/Gaithersburg; (f) Green Line to National Harbor; (g) Yellow Line to Lorton; (h) Silver Line further to Leesburg.

And more infill stations: (1) Montgomery College on the west Red Line; (2) Kansas Avenue on the east Red Line; (3) Oklahoma Avenue on Blue/Orange (this station was planned in the original system but successfully opposed by residents); (4) St. Elizabeths Campus on the Green Line; (5) Eisenhower Avenue/Valley on the Blue/Yellow Lines.

Plus more interline connections.  Exploration of a Purple Line extension on New Hampshire Avenue to White Oak, and from New Carrollton to Alexandria.  And exploration of light rail in Upper Montgomery County (Corridor Cities).

Momentum: The Next Generation of Metro

Strategic Plan: 2013-2025 (published in 2013)

This plan is well done.  WRT Metrorail it suggests:

(1) possible extensions to Centreville (Orange Line in Virginia), to Bowie (Blue Line in Maryland) and to Potomac Mills (Blue Line in Virginia).

(2) a possible separated Blue line either more north between Rosslyn and H Street NE along M Street, or between Rosslyn and H Street via Constitution Avenue.

(3) A new platform station, separating the Orange and Blue Lines, for the Blue Line at Rosslyn

(4) Walkways between stations to foster foot-based transfers to stations in close proximity.  For example, this was proposed for Metro Center and Gallery Plan in a plan dating to 2002.  Later a walkway was suggested between Farragut West and Farragut North, to facilitate transfers without having to go to Metro Center.

(2) extension of the Purple Line south and west from New Carrollton to Virginia

There are also discussions about BRT, commuter rail, and streetcars, in keeping with various plans at the time, pursued by other entities.

Connect Greater Washington - Transit Project/Strategy Summary, 2016

My mind is too full to give this document adequate justice: part one; part two.  

(1) Another Circumferential Line connecting the ends and the suburbs, further north than the current Purple Line alignment, and then takes up the concept as is from New Carrollton.   While I picked it up from an Internet posting in 2008 it's in this 2016 document.  

It doesn't show a transfer connection to a Columbia Pike line, and it has more stations, 18, between the legs of 8 Metrorail lines, which are transfer stations on the map.  Whereas the "1991" map only shows 5 interstitial stations.  This map also shows the Purple Line connecting to the west leg of the Red Line at White Flint (now North Bethesda), not the Bethesda station, which is the eastern origin point of the line under construction.  It's not clear if the map shows a connection to Dulles Airport.

(2) And so many other possibilities:

• Making the Silver Line a Virginia only service, with a new station at Rosslyn (not recommended)
• WRT the Beltway line, sticking with Maryland's Purple Line light rail, but also with Virginia, extending from Bethesda to Tysons, and Tysons to Merrifield and more expansion in Maryland on the south
• Yellow Line separation once it crosses the Potomac, adding a station on the National Mall, not connecting to L'Enfant Plaza, having a transfer station at Union Station, and continuing up North Capital and Georgia Avenue to Silver Spring
• Separated Blue Line from Rosslyn to Union Station, maybe on H Street NE or a Separated Silver Line to Union Station, and then interlining on the Orange/Blue.  (It anticipated streetcar service would be provided on H Street, therefore it didn't need to be duplicated with direct Metrorail service.)
• Metro Center-Gallery Place and Farragut North-Farragut West underground pedestrian connections
• Blue Line extension to Potomac Mills
• It doesn't recommend extension to Bowie from Largo based on density, employment figures.  Below I argue that such an extension, even further to Annapolis, should be considered on economic and equity grounds, but as discussed it needs a commitment to development along that route.
• The infill stations not previously approved are not recommended.  However, the Oklahoma Avenue station could now be justified as a result of the Washington Commanders team returning to the RFK campus, with planned ancillary development.  A St. Elizabeths station could be justified by the since movement of the Department of Homeland Security to that site.

Extensions to Potomac Mills/Quantico

(Fairfax and Prince William Counties)

In keeping with the WMATA policy of jurisdictions being responsible for expansion planning, Fairfax County's Countywide Transit Network Study (2016) calls for extending the Blue Line to Potomac Mills in Prince William County.  

In 2021, the Virginia State Department of Rail and Public Transportation did a study (Springfield to Quantico Enhanced Public Transportation Feasibility Study) recommending extension of either the Blue or Yellow Lines to Quantico (Marine Base, CIA Training Center) and the end, also serving Fort Belvoir and Potomac Mills ("Here’s how Metro would change Prince William County development, if a Quantico extension ever happens," Washington Business Journal).

The State study said it was possible, but would take a decade or two to come about.  I prefer the Yellow Line alternative which serves the Rte. 1 Corridor, and doesn't require a big horseshoe bend to reach Fort Belvoir.

The BLOOP/Blue Line Loop, 2023

I always thought this was dumb, so I never really wrote about it.  I don't think I gave it enough credit, but I still didn't think it provided enough value.

-- Blue/Orange/Silver Capacity & Reliability Study

-- Alternatives

The preferred alternative would have provided an inner ring subway service providing a new platform at Rosslyn, some inner city stations in DC, and a connection to National Harbor in Prince George's County.  It added 8 stations in addition to transfer stations at Rosslyn, Mount Vernon Square, Union Station, and Navy Yard.

Although it called for service to Georgetown and 8 total new stations in DC, I didn't think that turning the line south from Union Station, rather than extending east from Union Station a la the original Separated Blue Line plan provided, enough value to DC.

OTOH a connection to Georgetown and an additional connection to Union Station were of high value.  And I could be biased because I lived in the H Street NE neighborhood for many years.  I still remember my shock reading the original Post article ("Crowds could derail success," 2001, and this article which preceded it, "Coming to a Curve: Region's Subway System Begins to Show Its Age, Limits"), when we were organizing the commercial district revitalization improvement program for the neighborhood, which has had great success.

But now, serendipitously from a transit service standpoint (not for taxpayers) the forthcoming football stadium at the RFK campus would also have been served by stations on the north side of the campus, not just from the RFK-Stadium/Armory station on the south.  

National Harbor is a blot of development with a casino, in Prince George's County, along the Potomac River across from Alexandria.  It's primarily accessed by car.

Although to be fair to WMATA, the BLOOP was satisficed, not optimized, but designed to get approval from all three jurisdictions: (1) Virginia for the new Rosslyn platform; (2) DC for connections to Georgetown, additional stations east of the current system, and a new connection to Union Station; and (3) National Harbor for Maryland ("Backwardness of transportation and land use planning: National Harbor, Prince George's County, Maryland | Why isn't high capacity transit access required from the outset?").

Light Metro

Nothing on the books, but current WMATA President Randy Clarke said in this "Ask me anything" session on Youtube, that if WMATA is to expand rail services, it'd most likely be light metro, like the expanding REM system in Montreal.  

A Reseau express metropolitan (REM) train on a test run in downtown Montreal.  

Photo: Canadian Press/Christinne Muschi.

Light Metro is light rail on a dedicated track, with automation.  In Montreal it's both above ground, and below--as they took over a tunnel used by regional rail. Then again, DC itself has failed with streetcars ("DC makes yet another bad decision about streetcars: will replace the one line with a so called "fancy" bus | The Vision Thing").   

Note that while REM gets a lot of attention these days, it's not a panacea ("Montreal's new, for-profit light-rail system: national model or cautionary tale?," Canadian Press) especially because the province agreed to pay the vendor 75 cents per kilometer per passenger for 99 years--that's $7.50  Canadian ($5.25 US) for a 6 mile trip.  That seems unsustainable.

Other unplanned but reasonable concepts for extension

Looking at the big map, I'd say you could also consider this extension but it's never been a part of any official planning.  

• instead of rerouting the Yellow Line to Silver Spring, I'd send it out New Hampshire Avenue into Montgomery County perhaps further along Colesville Road -- this combines a couple of different ideas in various plans
• Adding a Yellow Line station in the vicinity of Jefferson Memorial on the National Mall is enough value to separate the Yellow Line as listed in planning documents referenced above.

Conclusion.  If you don't plan for extensions or infill stations (system intensification) you don't get them.  If you propose dumb ones you don't get them either.  If you propose and plan for good additions to the transit infrastructure, with a jurisdiction in support, you'll get them.

But because it always costs much more to wait, it's better to move forward more quickly.  Costs balloon up to 5x or more if you don't.

WRT the various iterations of official plans of some sort (plus some of my own) this is what I would have prioritized, recognizing that my bias is on intensification of adding stations in the core, which is likely to result in the most ridership.

• A Wheaton-Georgetown-Manassas Line serving Columbia Pike, with 12 stations, including Georgetown and Kennedy Center

This would provide 7 new stations in DC, and would support intensification in the Columbia Pike corridor.  Southern Tower apartments would finally get their Metrorail connection.

(We won't talk about the failed Columbia Pike Streetcar project, "Arlington officials halt efforts on streetcars for Columbia Pike, Crystal City." Washington Post.)

• Separated Blue (or Silver) Line

This would provide new platforms/connections at Rosslyn and Union Station, service to Georgetown and to the H Street NE corridor, which given the forthcoming stadium for the Washington Commanders at the RFK campus, adds transit capacity to a future high in demand destination.

My Separated Silver Line concept does this, but also adds stations along Arlington Boulevard in Arlington, which is also an intensification move.  Same with a potential leg north on Bladensburg Road potentially into Prince George's County.

• Various line extensions

Like Shady Grove to Germantown, Orange Line to Fair Oaks, etc., make sense to me.  Counties should be looking out for their interests, and at least doing scoping to determine if such extensions make sense. Like what Fairfax County did with its transportation plan, calling for a Blue Line extension.  As the "not recommended" language in the 2016 plan makes clear, these areas need more population and employment density to justify the extension.

But, if you don't plan for them, they certainly won't happen.

• Orange Line to Annapolis:  Also an economic development equity move

It's far, 28 miles from New Carrollton.  

But it's an important regional destination, especially being the State Capital, given limited bus service and no railroad service,  adding connections to Bowie on route, setting up the conditions for intensification, etc.  (Hell if we're really dreaming then you could do a Metrorail line from Annapolis to Baltimore, or alternatively a new Baltimore Subway Line to Annapolis, 30 miles.)

I went to a conference in Annapolis in 2005 and people were opposing a new development there because of how much motor vehicle traffic it would generate.  I was thinking, "this is so much different from DC, because you can build this close to a Metrorail station and generate so much less automobile traffic."

It should also be prioritized on economic development equity grounds ("D.C.-area leaders consider prioritizing equity in transportation and land use planning," Washington Post).  Like most regions, the economic center of the Washington region continues to shift West ("A Region Divided: The State of Growth in Greater Washington, D.C." Brookings).  This would provide the ability to intensify on the East side of the metropolitan area.

Prince George's would have to finally prioritize transit oriented development to make this work for them.

-- "Better late than never? DC Metrorail Blue Line Corridor Coalition advocates for TOD, 45 years after line opens" (2025)

--"Prince George's County's newly announced transit oriented development program for the Blue Line," 2022
-- "Backwardness of transportation and land use planning: National Harbor, Prince George's County, Maryland | Why isn't high capacity transit access required from the outset?," 2022
-- Branding for Downtown Largo, Maryland National Park and Planning Commission
-- "Major Blue Line projects aim to transform Prince George’s County. Residents hope it’s for the better," WAMU/NPR
-- Ten Principles for Developing Successful Town Centers, Urban Land Institute, 2007

-- "The future of mixed use development/urbanization: Part 3, Prince George's County, where's the there?," 2011
-- "A recommended new planning direction for Prince George's County," 2011
-- "Another lesson that Prince George's County has a three to five year window to reposition based on visionary transportation planning," 2011
-- "Frustration #3: the talk about transit oriented development and Prince George's County," 2013
-- "Prince George's County still doesn't get "transit oriented development" and walkable communities: Greenbelt edition," 2012

-- "Making over New Carrollton as a transit-centric urban center and Prince George's County's "New Downtown" (2017, originally 2014)

Also it would connect to the Purple Line, and if the Purple Line were extended from New Carrollton to Alexandria, it would be even better.

Would it be cool if Metrorail were extended to Annapolis, and Baltimore Subway to Annapolis, ideally as part of a greater plan ("Transit planning in Baltimore").

• Purple Line.  

I don't think a circumferential line would have generated the kind of ridership necessary to justify the cost of heavy rail, unless like how the Moscow subway is prioritized by the national government, it was funded regardless of strict economics.  However sections in Virginia probably would have generated decent ridership as the line would reach underserved areas.

I do think planning for further phases, especially in Prince George's County, and from Bethesda to Tysons ought to be considered.  Definitely from New Carrollton to Alexandria.  PG County should make the latter one of its top economic development priorities. 

• Yellow Line from Fort Totten up New Hampshire Avenue into Montgomery County and then on Colesville Road

This is my concept, never has been studied formally.  It's a way to serve an intensifying corridor and major employment centers like White Oak, and would connect to the Purple Line light rail at Takoma/Langley Crossroads. 

(A blogger at Greater Greater Washington suggested an alternative going up Georgia Avenue to Silver Spring.  To me, it would make more sense if it were extended beyond that station.  "Imagine a Separate Yellow Line."  And I'm not sure you can get the intensification benefits, without going to an Arlington Planned Unit Development underlying property upzone.)

• BLOOP

I never gave it a chance.  Basically it's an inner circumferential line.  It would be in DC's favor, adding service to unserved areas like Georgetown, connecting Rosslyn to DC, adding new transfer stations at Union Station and Navy Yard (Washington Nationals Stadium) and stations in both the NW and SE quadrants.  Plus it provides subway service to some locations in PG County, including National Harbor.

• Extension to Quantico by either the Blue or Yellow Lines

Not my ballgame.  It's super polycentric and exurban.  But it will reach some major employment centers and could provide some interesting opportunities for in-line transit service if more stations are added in certain places, comparable to intra-Arlington County ridership between Rosslyn and Virginia Square Stations.  Nonethess for Fairfax and Prince William Counties, it could be a top economic development and transportation planning priority ("Reimagining Potomac Mills: County’s draft comprehensive plan envisions big things for Prince William’s busiest mall," Prince William Times).