Tuesday, July 28, 2009

Where the Metro Riders Are, and Aren't

How full are Metro’s trains at any point in the system? What routes do riders take when confronted with a choice between two transfers, or between a longer one-seat ride and a transfer? Last year, in discussing I created about the proposed Blue Line reroute, a reader asked about this, but Metro hasn’t collected the data.

To answer this question, classmate and frequent GGW commenter Reza and I created a non-scientific survey, and used the data to build a diagram of passenger traffic on Metro system. This survey was unscientific and the results should not be considered as absolute facts. It does show potential trends, but a larger and broader sample would be necessary to validate these results.

The survey first asked respondents to state a certain preference, like the top factor they use to decide on a route. Later, it presented a specific scenario and asked respondents which route they would choose. Overwhelmingly, survey respondents primarily prioritized getting to their destination in the shortest time. A plurality of 44 percent chose minimizing transfers as the second most important factor. For the third choice, a plurality of 37% said, given the option, they’d choose a line with more frequent trains.

Based on the responses, Reza and I created a decision tree to assign the trips from the 2007 Ridership Survey to the links of the Metro system. On the segments of the system without alternative routes, the diagram is 100% accurate from Metro’s origin and destination data. For example, ridership between Takoma and Silver Spring is definitely almost twice as high as between Silver Spring and Forest Glen, which is why Metro turns back half of Red Line trains at Silver Spring.

Inside the area with alternative routes (bounded by Fort Totten, Metro Center, L’Enfant Plaza, Rosslyn, and Pentagon), the diagram relies on the non-scientific and possibly non-representative survey.

This information is very important to helping Metro make good decisions about service. Dropping the percentage of rush hour Blue Line trains at Rosslyn 40 percent to only 20 percent, as Metro proposes, would make the most sense if about 80 percent of riders at Rosslyn were on the Orange Line. But some readers of Greater Greater Washington and elsewhere commented that their Blue Line trains between Rosslyn and Arlington Cemetery seem pretty crowded, and that they probably would become even more so if Metro halved the number of trains.

Metro’s May 2007 ridership survey lists the number of trips made from any station to any other station, on average, but not which path riders take to get there, when they have a choice. We don’t know what emphasis riders place on factors transferring versus travel time, and therefore can’t ascertain what routes people would choose if given an option. Of course, a trip from Shady Grove to Dupont Circle can only happen via the Red Line, but from Van Dorn Street to L’Enfant Plaza, the rider has to choose between the one-seat Blue Line ride and a transfer to Yellow, or a trip from Woodley Park to Prince George’s Plaza involves a transfer at either Fort Totten or Gallery Place.

Metro needs accurate models to make decisions about service levels given its budget and infrastructure constraints. They periodically take a statistical sample of riders to determine where people are boarding, where they’re exiting, and how they get to and from stations. But they have little data about how people get from point A to point B. One method that Metro uses to determine the ridership on certain line segments is to station workers on the platform to count passengers on trains, but this doesn’t capture all information about route choices. WMATA should consider adding those questions to their ridership surveys.

The ridership per link estimated by our survey and assignment model show some interesting relationships.

As mentioned above, ridership drops by half on trains going northbound through Silver Spring. The decision to short turn trains there (because of the presence of a pocket track) was a good one. The phenomenon does not repeat itself on the other side of the Red Line. Volumes never drop significantly at any one stop, although they do taper as the line approaches Shady Grove. During rush hours, half of all trains turn back at Grosvenor, but unlike at Silver Spring, there is no major drop off in volume there. In fact, there are more riders in the link south of Grosvenor than there are in the link south of Silver Spring and ridership is higher at every single link north of Grosvenor than it is on the link between Silver Spring and Forest Glen.

Downtown, the Red Line is very busy. As one would expect, there is a significant jump in ridership at Union Station when coming from Glenmont. Ridership jumps by almost half from the link north of Union Station to the link south of Union Station. It might be worthwhile to find a way to insert a pocket track into the southern tip of Brentwood Yard and run some rush period trains from Shady Grove to New York Avenue.

In Virginia, there are significant drops in ridership west of Ballston and west of West Falls Church. West of Ballston, ridership drops by approximately one-quarter, and then by another third west of West Falls Church. Currently Metro does operate some trains from/to West Falls Church during peak periods. It might be helpful, especially after the Silver Line opens, to construct a pocket track in the median of Interstate 66 between Ballston and East Falls Church. This would allow some trains from or to downtown to serve the crowds of the Wilson Boulevard corridor. This will be especially important once the SIlver Line starts to reach ridership targets because Arlingtonians will find it harder to get on already crowded trains from the suburbs.

Volumes also drop on the Blue and Yellow Lines south of King Street. The combined ridership south of King Street is 20 percent lower than on the segment north of King Street.

What about Rosslyn, the spot which started this whole endeavor? Based on our analysis, of the riders traveling on the two links immediately outbound from Rosslyn, 62 percent are on the Orange Line and 38% are on the Blue Line. This matches closely current service levels.

At Pentagon, a similar look shows us that of passengers traveling on the two links inbound of the station, some 54 percent are on the Blue Line and 46 percent take the Yellow Line Bridge. This also closely matches current service levels.

This brief analysis demonstrates some of the difficulties with understanding ridership patterns on the Metro. It shows why it is so important for Metro to find some way of surveying patrons on how they travel, not just where they travel. Unfortunately, because of the limitations on our surveying it is difficult, if not impossible, to draw substantive conclusions about ridership patterns themselves. However, it does offer an interesting glimpse at a better way to plan for service alterations.

*Commenting has been disabled. Please comment on this same post at Greater Greater Washington.

Thursday, July 23, 2009


I grew up in North Georgia, not too far from sprawling Atlanta*. Even Atlantans know that it is the poster child for "dumb" growth in America (perhaps in the New World). Yet the region continues to swallow up farms and forests at an alarming rate. Despite growing environmental consciousness and rising gas prices, most Atlantans don't see any reason to change their behavior. Others have made the choice to live a more urban lifestyle. When I moved to the big city for the first time, that's what I did. I lived right in the heart of it all, just across the Downtown Connector from Midtown.

In the Big Peach, they've come up with a moniker to reflect this dichotomy. I am, of course, referring to the ITP/OTP distinction. You see, I lived Inside the Perimeter (ITP), which is what we call our Beltway, Interstate 285. Like others living inside the circumfrential highway, I viewed the suburbs as frightening and concieted (e.g. Scarietta, county seat of Snobb County) - they were a place I rarely ventured. We ITPers viewed suburbanites (Gwinnetians, Cobblodytes) as people who don't care about their actions. People who belch exhaust from their giant SUVs while cruising on 6-lane arterials to go the nearest store (which is usually a supermarket) for a few items. People who come into the city for work, but won't be caught dead there after 6:30P (probably because they fear that they will get killed if they do stay that late).

But OTPers have their own preconceptions about ITPers. After all, we all are pretty much liberal-pinko-commies who only shop at Whole Foods and go everywhere on our bikes (or so they say). We are the ones alone who can differentiate between the 71 different Peachtree streets (West Peachtree, Peachtree Battle, Peachtree Industrial, you get the idea...) ITPers are always championing kooky causes like transit expansion, peace, and an end to sprawl.

And so ITPers and OTPers face off across the 8-lane trench of a freeway which has come to symbolize the mental divide within the region. As an "insider" I always saw ITP as a badge of pride. Living the urban lifestyle was something of which one could and should be proud. I doubt that OTPers saw us the same way. For them the distinction was probably less clear. After all, most of the world is outside of Atlanta's Perimeter. Certainly most of the region is. Anyway, while we ITPers always looked at OTPers with disdain, I don't imagine that OTPers were too broken up about it.

But I left Atlanta. I moved to Washington, where the Beltway is not seen as a wall between city and suburb, but rather as a barrier between "Washington" and "Uhmaricuh". Politicos and pundits from around the nation disparige Beltway Insiders as disconnected from the pulse of the nation; as representative only of special interests. And since they've stolen the term, we can't use it to define the city/suburb lifestyle choice.

During my first two years here in Metropolitan Washington, I lived inside the Beltway. I saw the Beltway much the same as I saw the Perimeter, but the distinction was not so clear. Here, the dichotomy between city and suburb is more blurry. This is probably due mainly to the politics. In Atlanta, 285 is seen as a dividing line between Democratic and Republican voters. In Washington, even the suburbs are fairly liberal. Besides, the region as a whole is far denser than Atlanta - even the Washington suburbs, on average. Of course, you'd probably have a difficult time telling the difference between Loudoun County, Virginia and Forsyth County, Georgia.

But I suppose the primary difference is that in Atlanta, being from Inside the Perimeter is a badge of pride. In Washington, being Inside the Beltway is not a term of endearment.

Even though I don't mind the Beltway moniker, I can no longer brag about my ITP status.

I've moved to a wonderful little town, just outside the Beltway. This place was an experiment in Planning long before anyone thought a superhighway ring-road was necessary; long before anyone even thought of superhighways (at least outside of Germany). I've moved to Greenbelt, Maryland, one of the best preserved examples of New Deal-era urbanism in the country. And while I don't live in Old Greenbelt, the original planned community, I'm only a few minutes away on foot.

I still am slightly anxious about my new status. (What will my ITP friends say? What will my readers say?) But overall, I know my life hasn't changed all that much. I'm still transit dependent and I'm still as devoted to liberal causes as always. But I am a little more disconnected from the city, from the amenities that make urban life great.

Greenbelt is not devoid of some of those amenities, however. It is a bastion of activism and liberalism, after all. And considering its roots in the New Deal, it's no wonder. That's probably how it got its nickname - the Peoples' Republic of Greenbelt. I have no doubt that I'll fit in well here. But I do wish the buses came more frequently.

*Note: The place where I grew up is now a part of sprawling Atlanta, although it wasn't really when I was growing up there.

Thursday, July 16, 2009

A Diagram is not a Map

I was reading one of Dr. Gridlock's entries yesterday morning when one of the comments caught my eye. Yesterday, Dr. Gridlock talked about Monday's HOR subcommittee hearing on the June 22 accident on the Red Line. In particular he said this:
Until Metro is sure that all trains can be detected by its electronic protection system, it will send only one train at a time through the crash zone between Takoma and Fort Totten. Next time you're riding, look at a Metro map to see how long a stretch of track that is. It's one of the longest gaps between stations in the entire system. Trains would normally be able to reach 59 mph between them.
The commenter that piqued my interest, Chris737, had this to say:

Of course, with its perfectly staight lines and 45 degree angles, the Metro diagram is more of a work of art than a map to scale....The distance between
Takoma and Ft Totten is about the same as the distance between all of the other
station pairs north of Brookland.
And he's right. The section of track between Fort Totten and Takoma is not really that long. The problem is that when many people envision the region, they think of the Metro Diagram. Let's not pretend that it's a map; because it isn't - not really. It distorts distance, and Dr. Gridlock should know that.

Of course, all maps distort distance to some degree. After all the world is round-ish and maps are flat-ish and square-ish. Technically speaking the Metro Diagram is a topological map, but in my opinion, is so far removed from geographical reference as to defy the term "map."

See for yourself:

Anyway, I decided to look into it. As it so happens, of the 88 "links" in the system, the "link" between Fort Totten and Takoma is the 16th longest at 1.92 miles. It is slightly longer than the 1.22 mile average distance between stations systemwide. I wouldn't say that it was "one of the longest gaps between stations." Of course that doesn't invalidate Dr. Gridlock's key point, namely that trains travelling between those stations normally do reach 59 mph.

Here's a look at the top 20 longest segments in the system:

  1. King Street to Van Dorn Street: Blue Line: 3.83 miles.
  2. Van Dorn Street to Franconia-Springfield: Blue: 3.56 miles.
  3. National Airport to Braddock Road: Blue/Yellow: 3.03 miles.
  4. Rockville to Shady Grove: Red: 2.62 miles.
  5. Stadium-Armory to Benning Road: Blue: 2.57 miles.
  6. Dunn Loring to Vienna: Orange: 2.51 miles.
  7. Ballston to East Falls Church: Orange: 2.50 miles.
  8. College Park to Greenbelt: Green: 2.45 miles.
  9. West Falls Church to Dunn Loring: Orange: 2.40 miles.
  10. Pentagon to L'Enfant Plaza: Yellow: 2.27 miles.
  11. Stadium-Armory to Minnesota Ave: Orange: 2.12 miles.
  12. Medical Center to Grosvenor: Red: 2.11 miles.
  13. East Falls Church to West Falls Church: Orange: 2.09 miles.
  14. Twinbrook to Rockville: Red: 2.08 miles.
  15. Prince George's Plaza to College Park: Green: 1.97 miles.
  16. Fort Totten to Takoma: Red: 1.92 miles.
  17. Fort Totten to West Hyattsville: Green: 1.91 miles.
  18. Cheverly to Landover: Orange: 1.82 miles.
  19. Friendship Heights to Bethesda: Red: 1.82 miles.
  20. Wheaton to Glenmont: Red: 1.77 miles.

But here's the rub; the sore spot that is causing friction between Dr. Gridlock and myself.

*NOTE: For the purposes of the rest of this discussion, I'm measuring the WMATA
printable map, available on their website, printed on 8.5 x 11 inch paper. In
this case, the distances are scalable upward, but their relationship to the real
distances remains absent no matter what the size of the diagram.

While the track between Fort Totten and Takoma has a distance of 1.92 miles, half the distance of the link between King Street and Van Dorn Street, on the diagram, Takoma is 2.0 centimeters from Fort Totten. Van Dorn is 3.1 centimeters from King Street - Not 4.0.

Additionally, if we're to use Dr. Gridlock's metric, please note that the distance (from the center of the station "dots") between Metro Center and Gallery Place is just under half of the distance between King and Van Dorn Streets on the diagram. In reality, the 3.1 miles between King Street and Van Dorn Street dramatically dwarfs the mere 1700 feet between Metro Center and Gallery Place (center of platform to center of platform).

Let's consider the Orange Line in Arlington (Orangington?) and Fairfax Counties. Each station between Court House and Vienna has the same separation on the diagram, 0.55 centimeters. However, while they all appear to be the same distance apart to someone only familiar with the schematic Washington popularized with the 1976 subway map, the actual distances vary greatly. The stations within the Rosslyn-Ballston Corridor are within walking distance of each other, but those far outside the urban core are much further apart. Between Court House and Ballston, distances are approximately 1/2 mile. Beyond Ballston, distances increase to over 2 miles between stations. The range? The shortest distance is between Clarendon and Virginia Square at 0.47 miles. The longest distance is between Dunn Loring and Vienna at 2.51 miles, the 6th longest distance between stops in the system.

But don't expect Metro's system diagram to tell you this.

You don't need to know anyway. Overly complicated maps can be the bane of travelers. Just take a Metro bus map, for instance.

And we've known this for many years. In fact, the topological map of the London Underground, designed by Tube worker Harry Beck in his spare time in 1931, set the standard for other systems, including Washington. But they don't always turn out to be as popular as one would think.

The geography-distorting Vignelli Map of the NYC Subway lasted from 1972-1979, and can be seen in period films such as "The [original] Taking of Pelham One Two Three" and "The Warriors." But the current map showing trains curving around the geometric jungle of New York won out. Even now, MTA is fighting against anything less accurate than pure geography - like the Kick Map, for example.

But in our case, a topographic map works just fine. In fact, it has become a major identifier of our region since its inception over three decades ago.

Just don't think that it represents the true geography of the region.

Friday, July 10, 2009

Cartographic Humor: "Patomic"

I like maps. I always have been facinated by them, and as a result I spend a lot of time looking at them. Occasionally, I come across a bit of funny business. So, I'm starting a new occasional feature to make a note of "Cartographic Humor."

Our first entry comes from right here in the District of Columbia.

Look at the labeling for East Potomac Park, the green area to the left of the Washington Channel. Yes, you're reading that (in)correctly. "Patomic" is not the correct spelling of this broad waterway or the adjacent park.

It's especially ironic since the golf course located in the park has the correct spelling, "Potomac."

See it for yourself at Google Maps.