Posts Tagged ‘greater greater dc’

Washington’s Systemic Streets (GGDC, Track29)

Thursday, August 13th, 2009

[Editor's note: Since moving to Washington, DC, neigh on 7 years ago, I have been fascinated by the system of street names used in the nation's capital. There's your normal east-west, north-south grid sectioned into cardinal quadrants in the NW, NE, SW, and SE directions, and then all the state streets, often large Avenues, named after the 50 first-order administrative units that form these United States. The above map shows where these are (some are tiny!), and the entire post, from GreaterGreaterWashington and 29Tracks, has more maps and dialog including a tidbit about the 1st thru 3rd rings being based on number of syllables and the 4th ring based on plants. Thanks Laris!]

Republished from GreaterGreaterWashington and Track Twenty-Nine.
Aug 7, 2009. By Matt Johnson.

Visitors and residents of Washington, DC know, to one degree or another, about the city’s street naming conventions. Most tourists know that we have lettered and numbered streets. And to some degree, they know there is a system, but it doesn’t stop them asking us directions. But most out-of-towners and even many residents don’t understand the full ingenuity of the District’s naming system.

Washington is partially a planned city. The area north of the Potomac and Anacostia Rivers and south of Florida Avenue (originally Boundary Street) is known as the L’Enfant City. This area of Washington was the original city of Washington, laid out by Pierre L’Enfant and Andrew Ellicott. It is comprised of a rectilinear grid with a set of transverse diagonal avenues superimposed. Avenues frequently intersect in circles or squares, and the diagonals create many triangular or bow tie-shaped parks.

Washington is the seat of government of a nation. Believing that the structure of the government should inform the structure of the city, L’Enfant centered the nascent city on the Capitol, home of the Legislative (and at the time, the Judicial) branch of the government, the one the framers held in highest esteem. From this great building radiate the axes of Washington. North and South Capitol Streets form the north-south axis; East Capitol Street and the National Mall form the east-west axis. These axes divide the quadrants.

The axes also provide the basis for the naming and numbering systems. Lettered streets increase alphabetically as they increase in distance both north and south of the Mall and East Capitol Street. Numbered streets increase in number as they increase in distance both east and west of North and South Capitol Streets.

Continue reading at Greater Greater Washington . . .

Visualizing Bus Level of Service (Greater Greater DC)

Monday, December 8th, 2008

[Editor's note: Looking at the previous post on visualizing subway level of service, I was reminded of one of David Alpert' great posts on the same topic in March 2008 but on the frequency and reliability of bus routes. David based his graphic on observed data but then extrapolated it a bit and graphed the resulting histogram. Also see this crazy art project showing 3D data sculpture of the Sunday Minneapolis / St. Paul public transit system, where the horizontal axes represent directional movement and the vertical represents time.]

Republished from Greater Greater DC.

Waiting for the L2

The L2 bus travels along Connecticut Avenue from Friendship Heights, detours through Adams Morgan, down 18th and New Hampshire through Dupont, and then along K Street to McPherson Square. It also runs right past my window. I started keeping track of its actual times and compared them to the schedule. (Click image for larger version).

This chart shows how much time you are likely to wait at 18th and S based on when you show up. The darkest area is 10% of the buses: for example, at exactly 8:00, 10% of the time a bus will come within 3 minutes, but 90% of the time it will take longer than 3 minutes. The lightest area is 100% of the buses (that I’ve observed); at 8:00, 100% of the time a bus will come within 8 minutes (not bad).

The red dotted line represents the schedule. The WMATA trip planner reports that this bus should arrive at 7:48, 8:04, 8:23, 8:36, 8:48, 9:01, and 9:16. If all buses showed up exactly on time, the entire chart would coincide with the red line.

You can see that many of the triangular areas deviate to the left of the red line. That means that the bus often shows up early. If you get to the stop at 8:46, two minutes before the scheduled 8:48 arrival, 30% of the time the bus will show up within four minutes, but 70% of the time it will take 12 minutes or more because 70% of the time this bus shows up before 8:46. And it’s been as early as 8:41 (that’s where the tall light blue spike appears), which means to be safe and avoid risking a 23-minute wait for a 9:01 bus that may show up at 9:04, you have to arrive to the stop seven minutes ahead of time.

The tighter the triangle, the more accurate the bus’s appearances. As you can see, the 8:04 is pretty good, only deviating to the left (early) occasionally and then not very far early. At the same time, it’s not late much; the big dark triangle means that the bus isn’t usually more than a couple minutes late either. On the other hand, its light colored spike is very high, meaning that occasionally even if you show up a minute early you might be stuck waiting 28 or 32 minutes if the 8:23 is late.

The 8:23 and 8:36 appearances aren’t very consistent, leading to the lack of visible shape in those areas. Those buses are often early and often late, and several times have shown up within one minute of each other.

You can see all my data on this Google Spreadsheet. The first tab is my direct observations; the second tab is the calculated data that generated the chart.

In conclusion, the 8:04 is fairly reliable, while the later buses are not so much. WMATA is working on offering real-time bus info which would help since someone could see how much time actually remained until the next bus, and see this before leaving home. The other big recommendation I see from this data is for the drivers to try harder to avoid being early. They should wait at certain key stops until the correct departure time. That way, commuters could at least know for certain that if they showed up a minute or two before the bus’s scheduled arrival, they wouldn’t be left waiting at the stop for 20 minutes.

Visualizing Level of Service on Subway Lines (Track 29)

Monday, December 8th, 2008

[Editor's note: Washington DC has the second busiest subway system in the US after New York city. This series of visual diagrams show the network's topology and how to optimize routing to achieve a better level of service (quicker train frequency). Note how the time scale has been reduced to modular 12, easy to understand as a train every 2 to 6 minutes based on the number of colored lines thru each subway station.

DC's metro rail subway is convenient and affordable. But with more people using transit every year, the system is beginning to show signs of strain (heck, it's over 30 years old now!). The federal gov't just gave one of the last nods to construct a new line (dubbed the "Silver") connecting downtown DC to Dulles International Airport and farther out into the exurbs. But this does little to alleviate crowding on the original 5 rail lines .

How to squeeze the most capacity out of existing tunnels and switches? These excellent maps from Track 29 chart the current system and show how it might be tweeked to optimize the flow of passengers from point A to point B primarily on the Orange line, the most overcrowded, where a switching problem reduces train frequency thru the downtown central business district (CBD).]

Republished in part from Track 29.
(They have a much more complete technical discussion.)
First seen at Greater Greater Washington.

The first diagram represents WMATA’s current service pattern during rush hours. Colors represent each of the subway routes. More lines along a colored route represent better (more frequent) service. [Ed: not all stations shown, based on "rush" peak service.]

Based on the 135 second headway, WMATA can run 5 trains through a given segment of track every 12 minutes. Each the diagrams below represents a 12 minute interval during rush hour. Each of the lines on the diagram represents a train in each direction. Therefore, a trackway with two lines (like between Stadium Armory and Largo) represents a headway of 6 minutes–12/2. In other words, you’ll be waiting for a train for up to 6 minues. While on the Red line it would only be 2.5 minutes. [Ed: map seems to undercount Green line service.]

There are several choke points in the system, including at the Roslyn tunnel where the Orange and Blue lines converge and travel under the Potomac River into the District of Columbia.

Click to see larger.

The chief limitation for the Orange Line, as you can see here is the 4 minute headway on the Vienna-Rosslyn segment. Adding one train would reduce headways to 3 minutes and would add a capacity of 1000-1400 passengers for every 12 minute period. Any additional capacity is sorely needed, but the segment of track between Rosslyn and Stadium Armory is essentially at capacity.

Hence the so-called “Blue Line Split.”  Here’s what WMATA is proposing: [Ed: WMATA runs the Metrorail subway in DC.]

Click to see larger.

This results in better service on the Orange line, and equivelent service on the Blue, except for Arlington Cemetary station primarily used by tourists (there are no homes or offices at that station). Many Blue line riders actually need to transfer at Metro Center or L’Enfant stations or get to eastern downtown faster, so this may actually be a boon for them, too.

Click to see larger.

But, while that squeezes extra service, the naming convention of the lines becomes confused. Some propose renaming / rerouting the Blue and Yellow lines like so (below). This map reflects this and planned Silver line service.

Greater Greater DC has a full discussion of adding even more commuter rail service to the nation’s capitol.

Continue reading at Track 29 . . .