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Transit


Ask GGW: Why do some stations have side platforms?

Have you ever wondered why your Metro station has two side platforms instead of a single island platform? If so, you're not alone. Reader Sam Inman is curious, too.


Images by the author.
Why are some stations (I'm particularly interested in the subterranean stations) designed with the side platform design instead of the island?

Do you know if this is dictated by a topography/cost concerns? Or was there a design consideration that wanted to force passengers to make their decision at the mezzanine level rather than on the platform level?

Unfortunately, the answer is not simple. In practice, the layout can be influenced by a variety of factors, so there's great variation between transit systems. But there are some general rules that influence the layout (though they're not hard and fast).

Economics
In general, island platforms can be cheaper because they require less duplicative infrastructure. However, sometimes other technical factors can make side platform stations cheaper.

With an island platform, the station requires less vertical circulation. For example, Foggy Bottom only needs 1 mezzanine-to-platform elevator, since it has an island platform. But Farragut West needs 2 mezzanine-to-platform elevators, since it has side platforms. Staircases and escalators can do double duty at an island platform, but sometimes need to be duplicated at side platform stations.

Loading can also be an issue. For example, at a station that is very commuter heavy in the morning with passengers all traveling the same direction, a side platform station may have one platform that is very full and one that is completely empty. That's less efficient than an island platform, where the passengers can use the whole platform, even though they're primarily focused on one track.

But oftentimes these considerations take a back seat to the method of construction, which can also influence the station design.

Construction influences
For underground construction, if the line is cut-and-cover, it is often more cost-effective to build side platforms. With cut-and-cover construction, the tunnels are constructed by digging up the street, building the tunnels, and then rebuilding the street.

To build an island platform station with this method, it requires the two tracks be spread apart from each other (to give room for the platform). This requires more excavation than a side-platform station, which only requires the extra width for the length of the station.


The difference in excavation required for side versus island platforms. Graphic by the author.

So when subways are constructed using cut-and-cover, like along I Street around McPherson and Farragut Squares, stations often have side platforms.

On the other hand, when a subway line is deeper, and is bored through the ground, it often makes much more sense to have island platform stations. This is because when lines are bored, the two subway tubes are not directly next to each other. Since the tracks are already apart, when they get to a station, it's much easier to just put the platform between the tracks, rather than to pull the tracks together so the platforms can be on the outside.

This is the case for the deep stations along Connecticut Avenue and Wisconsin Avenue between Woodley Park and Medical Center.

It's much rarer, but sometimes both tracks are built in the same (larger) subway tube. This is the case for the Red Line between Farragut North and Woodley Park (not including either of those stations). Both tracks are in the same (bored) tunnel, and so at Dupont Circle, it makes much more sense to have side platforms, since the tracks are already right next to each other.

This is also the case for almost the entire Montreal Metro system, where the tracks are always in the same tunnel. As a result, almost every station has side platforms.

There's less pressure for one or the other design on elevated and surface rail lines, since the construction is cheaper than subway construction. However, there are still some influencing factors. For example, when the tracks are running in a freeway median, the road lanes have to spread out in advance of the station anyway, so there's no penalty for spreading the tracks out ahead of time either. So in that case, there's no penalty for an island platform station. For a side-platform station, the only penalty is the duplicated infrastructure.

On an elevated viaduct, it might be easier to have one structure carrying both tracks rather than two separate structures for each track, and therefore side platform stations may be cheaper, like at West Hyattsville. But then again, it's not necessarily better one way or the other, and so sometimes an island platform makes more sense, like at McLean.

Design decisions
Sometimes, though, a transit agency might make an intentional decision that overrides other concerns.

Terminal stations should have island platforms so that the next train can leave from either track. So any station that is planned to be a terminal for any period of time generally has an island platform. When a terminal does have side platforms, generally trains have to go out of service on one platform, go past the station, reverse, and then pull in on the other platform. That's very inefficient. Alternatively, passengers have to wait in the mezzanine and then pick a platform when the train is ready to depart, also inefficient. All of Metro's terminals have island platforms.

Any station that is likely to be a transfer between diverging lines should have an island platform. That way a passenger coming from one branch can transfer to the other branch simply by walking across the platform. This is the case at Stadium/Armory, where a passenger riding from Addison Road to New Carrollton can make an easy cross-platform transfer.

Furthermore, at key stations, certain platform arrangements can be more efficient.

Metro Center, Gallery Place, and L'Enfant Plaza are good examples. With right-side exits on the upper level, there can be multiple escalator shafts down to the island platform on the lower level. If both levels at these stations had center platforms, the only efficient layout would be to have a mezzanine between, which is how Fort Totten is laid out. And that's generally more expensive and less efficient. Though in the case of Fort Totten it works because the lines have such a great vertical separation (the Red is elevated, the Green is underground).

Other design factors
And while we don't have any examples of it in the Washington region, the "Spanish solution" can also be employed to reduce dwell times. The Spanish solution is where the doors on both sides of the train open. This makes it faster to unload and load the train. MARTA's Five Points station has this on both the upper and lower levels.

When looking at express/local configurations, having island platforms between the local and express tracks allow for an easy cross-platform transfer between trains going the same direction. But at some stations where express service needs to stop, but where the agency wants to discourage transferring passengers (because of crowding), the island platform can be placed between the two express tracks and with the local tracks having side platforms. This is the case at 34th Street/Penn Station on the 1-2-3 and A-C-E. That station is important enough that all trains need to stop, but the stations are crowded. The traditional island/island layout is present one stop north at Times Square/42nd Street to allow transfers between locals and expresses.


Graphic by the author.

In systems that have express/local tracks, there are even alternate ways to accommodate local stations. In New York, local tracks tend to be on the outside, so local-only stations have side platforms. The drawback here is that if the local service ends before the express service, it's difficult to turn those trains around, since they have to cross over the express tracks. The Lexington Avenue (4-5-6) Line handles this by having the local 6 train dive under the 4-5 express tracks via the City Hall Loop.

A rarer alternate version is to put the local tracks in the center. In this case, with the express tracks on the outside, the local-only stations have center platforms. This is present on Chicago's north side trunk, with the local Red Line in the center and the Purple Line Express running on the outer tracks.

So, as you can see, the logic is somewhat complicated. Sometimes it's cheaper to do one, sometimes it's cheaper to do the other. Sometimes, there are logistical reasons for doing one over the other. Sometimes, it may just be more-or-less random.

Transit


Here are the answers to whichWMATA week 19

On Monday, I posted 5 images of stations in other transit systems in a twist on the weekly whichWMATA challenge. Here are the answers.

We got 55 guesses this week. 27 of you correctly guessed each of the 5 transit systems shown here. 8 of you got all of the systems and all 5 of the stations. Great work, Austin, Roger F, David, Joe M, Mike B, Peter K, Matt D, and Paul Kirk-Davidoff.


Image 1: BART.

The first image is a picture of BART's 12th Street/Oakland City Center station. BART is the regional rail system in the San Francisco Bay Area, and is very much a sister system to WMATA. This station in downtown Oakland is distinctive with its red tile. Another clue is the "platform 3" label on the digital sign. 12th Street has 3 tubes because it's where several lines converge. 49 of you got BART right. 12 of you, appropriately, guessed 12th Street.

Several of you guessed 19th Street - Oakland, which has an almost identical layout. But the tile there is a dark blue color, which differentiates it from 12th Street (with red tile).


Image 2: Montreal Metro.

The second image shows art above the tracks at Montreal's Berri-UQAM station. Montreal's Metro has distinctive blue carriages with a white stripe, and that helped most of you narrow this one down. 36 correctly guessed Montreal. 19 got Berri-UQAM right.


Image 3: DART.

The third image shows a DART train at Victory station near downtown Dallas. Victory is the station near the basketball arena here and also serves as a transfer point to the TRE commuter train to Fort Worth. The landmark Reunion Tower is visible at center right. 45 knew this was DART. 15 got Victory station right.


Image 4: San Diego Trolley.

The fourth image shows a San Diego Trolley LRV leaving San Diego State University station. San Diego is home to the first modern light rail system in the United States, and the bright red cars are an icon of the city. The station at San Diego State is the only underground station in the system. 36 of you got San Diego. 15 correctly guessed San Diego State University station.


Image 5: Charlotte CATS.

The final image shows the Third Street/Convention Center station in Uptown Charlotte. This stop has beautiful red and green art that doubles as the station's canopy. 31 guessed Charlotte. 17 knew it was Third Street.

Next Monday, we'll have 5 more photos for you to identify. Thanks for playing!

Transit


WhichWMATA week 19: On vacation

This week, whichWMATA is on vacation, which means it's time for a real challenge. Can you guess the transit systems these photos are from? Earn a bonus point by also correctly guessing the station where the photo was taken.


Image 1


Image 2


Image 3


Image 4


Image 5

We'll hide the comments so that the early birds don't spoil the fun for the rest of you.

The answers will appear on Wednesday. Good luck!

Public Spaces


This could have been the Silver Spring Transit Center

Though it remains unfinished, the Silver Spring Transit Center has been in planning since 1997. But 20 years before that, architecture students created this proposal for a giant box stretching across downtown Silver Spring.


A 1970s proposal for the Silver Spring Transit Center. All images courtesy of Neil Greene.

Silver Spring is one of the region's largest transportation hubs, bringing together Metro, commuter rail, local buses, intercity buses, and eventually the Purple Line and the Capital Crescent Trail. Fitting all of those pieces presents a pretty interesting design challenge, and naturally attracts architecture students. When I was in architecture school at the University of Maryland, I saw more than a few thesis projects reimagining the transit center.


A section drawing of the proposed transit center, which would have also contained stores, offices, a hotel, and apartments.

Recently, Action Committee for Transit's Neil Greene found this proposal for the Silver Spring Transit Center produced by a group of architecture students at Catholic University in the 1970s, right before the Metro station opened in 1978. Like the most recent plans for the transit center, which have since fallen through, they surrounded the transit center with buildings containing apartments, offices, a hotel, and shops. Except in this proposal, they'd all be in one giant superstructure surrounding the station platform.

In their design, Metro trains would pull into a giant, skylit atrium, surrounded by shops and restaurants, with apartments, offices, and hotel rooms above. That was a really popular idea at the time, pioneered by architect John Portman, though I don't know of any atria that included a train station.


Metro trains would have passed through a giant atrium.

Directly below the platform was the B&O Railroad, the precursor to today's MARC commuter rail. Below that were buses, taxis, and a kiss-and-ride, as well as an underground parking garage for commuters.

The entire structure would have stretched over multiple blocks from Colesville Road and East-West Highway, where the NOAA buildings are today, up to Wayne Avenue, where the current transit center is. Existing streets would go through the transit center in underpasses, while skybridges would allow visitors to travel through the rest of downtown Silver Spring without touching the street.


Skybridges would have connected the transit center to the rest of downtown Silver Spring.

Of course, this was just a student proposal, and was never carried out. But Montgomery County did propose skybridges in downtown Silver Spring as early as 1969 and, by the 1970s, had drawn out an entire network of them, most of which were never built.

This was in keeping with the prevailing wisdom of the time, that cars and pedestrians should be kept separate. But as we've seen in places where this actually happened, like Rosslyn or Crystal City, this doesn't work very well, and those communities are getting rid of their skybridges.

Of course, had we actually pursued a design like this, the Silver Spring Transit Center might have actually opened by now. Repair work on the current facility is currently underway and Montgomery County officials say that it could open next year, just seven years after groundbreaking.

Public Spaces


With its new plaza, Tysons begins to feel urban

Metro's Silver Line isn't the only indication the transformation of Tysons Corner is clearly underway. Further undeniable evidence: The Plaza, a popular new urban-style open space at the front door to Tysons Corner Center mall.


All photos by Dan Malouff except where noted.

The Plaza (that's its official name) is on the north side of the mall, near the pedestrian bridge from the Tysons Corner Metro station. Three new high-rises are under construction around the plaza, tightly enclosing the space like a genuine city square.


The Plaza and its surroundings. Original photo by Macerich.

The pedestrian bridge to the Metro station isn't open yet, because the high-rise it connects is still under construction. But when all is said and done, The Plaza will become the main entry point to the mall from the Metro. In a very real sense it will become the center of this emerging urban neighborhood.

Befitting Tysons, The Plaza is a thoroughly contemporary update on the classic city square. There's no marble statue in the middle, no grand fountain like in Dupont Circle. Instead, there are padded couches, small-scale artistic flourishes, and outdoor games.


Couches (left), and sculpted birds (right).


Ping pong (left) and corn hole (right).

The first plaza-fronting retail, a Shake Shack, opened earlier this week. More is coming soon.

One crucial difference between The Plaza and a traditional city square is who owns it. This may masquerade as civic space, but it's clearly private property. Security guards patrol the square, and you can bet homeless people aren't welcome to sleep on benches.

But still, The Plaza is a big step forward for Tysons. It's a genuine gathering place, and people are using it. Even without the Metro connection, plenty of other people were hanging out nearby when I visited last weekend. It's not the kind of place that a mere 20th Century office park would support.

Cross-posted at BeyondDC.

Transit


Here are the answers to whichWMATA week 18

On Monday, we posted our eighteenth photo challenge to see how well you know Metro. Three of our readers took photos of different stations. Here are the answers. How well did you do?

We got 30 guesses on this post. Seven of you got all five. Great work, iaom, Patrick, Russell, Phil, Justin...., Peter K, and Adam H.


Image 1. Photo by DC Transit Nerd.

The first image is a picture of art at the Archives station. This installation is called "Ocean Piece" and is located in the entrance to the station. 24 of you got this one right.


Image 2. Photo by Sand Box John.

The second image shows Prince George's Plaza. This station's unique design is very distinctive, and 24 of you knew this one.


Image 3. Photo by DC Transit Nerd.

The third image shows a train standing on the platform at New Carrollton, viewed from the adjacent Amtrak platform. Clues include the yellow edge-of-platform strip on the Amtrak platform, and the parking garage, visible at far left. 21 of you guessed this one correctly.


Image 4. Photo by Ben Schumin.

This picture shows the entrance to Capitol South station. The clues here include the lack of a canopy above the escalators, the rowhouses visible in the distance, and the parking lot in the foreground. 13 of you got this one.


Image 5. Photo by DC Transit Nerd.

The final image shows a strip map at Gallery Place. WMATA tends to test out new signage at Gallery Place, and this is the only place on the Red Line where the strip map includes arrows showing the direction of travel. 10 got this one right.

Thanks to Ben Schumin, DC Transit Nerd, and Sand Box John for submitting photos! Thanks to all of you for playing.

Next Monday, we'll have 5 more photos for you to identify.

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