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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!

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.

Transit


More households near transit mean more transit riders

Pop quiz! Can you name the 5 Metro stations that have the highest number of households within a half-mile walk?

Here's a hint: More riders walk to those 5 stations each morning than to just about any others in the system.

It's not a coincidence. According to WMATA's PlanItMetro blog, "the more people can walk to transit, the more people do walk to transitand data across Metrorail stations prove it."

But there's at least one surprise: 3 of the 5 stations with the most households in a half-mile walkshed are in Maryland or Virginia, not the District.


Households and walk ridership per Metro station. Image by WMATA.

Columbia Heights has by far the most households within walking distance. That makes sense. It's one of DC's densest neighborhoods, and the Metro station is right near its center.

But the second most household-rich Metro station is Arlington's Court House. Rounding out the top 5 are Ballston, Silver Spring, and Dupont Circle.

All 5 of the most household-rich stations are also among the top 10 stations with the most riders who walk to the station each morning. The rest of the top 10 walking stations are Woodley Park, Cleveland Park, Pentagon City, Crystal City, and Bethesda.

More riders may be walking to jobs from the downtown stations, or from Rosslyn, but those are the destinations, where riders in the morning are getting off. The origin stations are the more residential ones.

All in all, Metro's stations fit neatly along a trendline that shows a strong correlation between more households nearby and more riders arriving to stations by foot.

Even the outliers tell a story. U Street and Mount Vernon Square have the 6th and 7th highest number of households nearby, but they underperform on walking Metro ridership. One might speculate that Mount Vernon Square is so close to so many offices that more people simply walk. U Street is a little farther away, but it's still close enough to downtown that buses and bicycles may be better options for a large portion of riders.

What else pops out as interesting?

Cross-posted at BeyondDC.

Transit


Photo: An actual bus running in the Route 1 transitway

This bus is not in service. But it is running in Alexandria's Metroway BRT corridor, presumably on a test run. It's pretty exciting to see the region's first BRT so close to starting.

The BRT opens for real on Sunday, August 24.


Photo by BeyondDC on Flickr.

Transit


Do you know the station? It's whichWMATA week 18

This week, it's time for a little something different on whichWMATA: Your entries. We picked the best five images from reader submissions. Can you guess the five stations these images depict?


Image 1. Photo by DC Transit Nerd.


Image 2. Photo by Sand Box John.


Image 3. Photo by DC Transit Nerd.


Image 4. Photo by Ben Schumin.


Image 5. Photo by DC Transit Nerd.

In the future, we'll have more reader submissions, so while you're riding Metro keep your eyes (and cameraphones) peeled for unique stations and architectural features.

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!

Transit


DDOT's 5-point plan to improve 16th Street buses

DDOT isn't yet willing to install a bus lane on 16th Street, but the agency is moving forward on a host of other improvements, and will study a bus lane next year.


Photo by BeyondDC on Flickr.

The 16th Street bus line is bursting at the seams. It carries more than half of rush hour trips on 16th Street. But the buses are slow, and they're so full that riders in the city's close-in neighborhoods often can't board.

Advocates have been pressuring for bus improvements on 16th Street since 2010. ANC Commissioner (and District Council candidate) Kishan Putta has championed the cause. Now, DDOT has adopted a 5-point plan to fix 16th Street.

Here are the 5 points:

Already complete: Signal optimization pilot program: In July 2014, DDOT retimed 44 of the traffic signals along 16th Street to improve their efficiency. After a few weeks of results, it appears to have sped up traffic (including buses). DDOT will continue to evaluate the results the rest of this summer.

August 2014: More articulated buses: Metro will reshuffle its bus fleet, to provide more long "accordion" buses on 16th Street. WMATA will move the articulated buses currently running on the Y series in Maryland to the 70 line in DC, then move the articulated buses currently on the 70 line to 16th Street. The Y series will have shorter buses, but they'll come more often.

Fall 2014: Longer rush hour operations: DDOT is considering extending the hours of rush hour parking restrictions on 16th Street, to keep more travel lanes open up to an hour longer in each direction. That will keep two lanes open to moving traffic, including buses.

Mid 2015: Transit signal priority & full optimization: By mid 2015, DDOT will expand its signal optimization pilot program to the entire corridor, and install new software that instructs traffic signals to hold a green light a few seconds longer if a bus is about to pass through an intersection. That will speed up buses along the route, so they're less likely to have to stop at red lights.

2015-2016: Bus lane study: Beginning in 2015, DDOT will begin a comprehensive study of transit improvements along 16th Street, including the potential for bus lanes and other long-term construction projects. The study will take about a year to complete, meaning 2016 is the earliest DDOT could install bus lanes.

None of these 5 points are new. DDOT has been working on them all for some time. But it's good to have them listed all in one place.

Cross-posted at BeyondDC.

Transit


Metro locks out an entire College Park neighborhood

Metro's aggressive rebuilding program sometimes means riders must use bus shuttles to travel to and from closed stations. But when Metro closes Greenbelt station, the work blocks access to the shuttles from an entire neighborhood.


Left: Walking path from Hollywood to Greenbelt on normal days. Right: When the station is closed. Maps by the author.

Greenbelt Metro station sits on the boundary between the cities of Greenbelt and College Park. On the Greenbelt side there's a bus loop and a massive parking lot. But few people live within a reasonable walk. On the College Park side is Hollywood, a neighborhood of single-family homes straddling Rhode Island Avenue. A pedestrian tunnel beneath the tracks links the two.

Right now, Metro is building a test track for new railcars between College Park and Greenbelt. This means construction most weekends, and sometimes Metro closes Greenbelt station for the work. So far in 2014, Greenbelt has been closed on 3 weekends. It will likely close again before the year is out.

As usual when Metro closes stations for weekend work, they provide bus shuttles to the nearest Green Line station that's open.

But there's a problem: When Metro closes Greenbelt station due to work, they lock the station gates. The pedestrian tunnel linking Hollywood is behind these gates. So when the station is closed, the tunnel closes too.

This means people who live in Hollywood can't even walk through the station to get to the shuttle buses substituting for trains. They also can't access regular buses going to places like New Carrollton, the University of Maryland, or Wheaton.

When Greenbelt station is closed, what's usually an easy 4 minute walk through the station becomes a daunting and impractical 1 hour 9 minute walk of 3.5 miles.

College Park station is different

College Park station, the next one down the Green Line, has a similar design, except for one crucial difference: the pedestrian tunnel under the tracks at College Park emerges outside the station gates, and so then tunnel can remain open even when the station is closed.

Greenbelt's tunnel isn't so lucky.


Tunnel at College Park. Photo by the author.

Can Greenbelt change?

Is there any way for WMATA to make sure riders who live in Hollywood still have reasonable access to buses, even when the station is closed? Ideally the agency could leave the station gates open at Greenbelt, and just block off the faregates with a barricade.

That might mean Metro has to have one more staff person at the station on work days, but locking out most of the people who live within walking distance of the station isn't a good option.

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