Recently in Networks Category

Two times in two days last week I was asked to fly to an east coast city for a half-day meeting. The meeting organizers offered to pay my travel expenses. I asked to save the travel money and tele-conference in via some/any web-based video technology. The organizers declined, saying they weren't set up to do that.

Seriously, you can pay more than a $1000 to bring me in considering airline tickets, hotel, ground transportation, and meals, but you can't get your act together to have a room with wireline internet, a camera enabled laptop (aren't they all now), and Skype or FaceTime or Google Hangouts or any of a hundred other services at a marginal monetary outlay of zero and a time outlay of damn close to that?

I hypothesize one source of the problem is the technological backwardness of the governmental/consulting/advocacy/transportation sector. This is a process of mutual causation. Technological backwardness deters the technologically advanced from entering the sector, reinforcing the backwardness. It's a wonder there are PCs on people's desks. It's no wonder we see no progress. I fully anticipate major changes to the transportation sector to come from outside actors, much like the Google self-driving vehicle because of this innovation aversion.

The second source of the problem might be incentives. I hypothesize the meeting organizers budgeted for travel, and not for information technology. They have no incentive not to spend the budget, the money has to get spent.

The third source of the problem is also incentives. My travel time costs them nothing. My video conferencing takes them a few minutes. No matter their few minutes are a lot less time than my travel, they (not me) are spending it.

I realize video-conferences are not quite as high a resolution in audio or video as being present, and in the hands of the incompetent have meeting-disruptive technical difficulties. But they are good enough for the purposes of this kind of conversation, for which conference calls are often used.

It is not that I object to spending your money, or actually want to save you money. I am not noble in this regard. It is that travel is a major hassle, filled with danger and uncertainty. This is often not worth it for me anymore especially for a less than one-day meeting in a city I have seen plenty of times where I am doing you a favor by being present (you asked me to attend, not vice versa). Moreover, I don't want to eat another dinner at an east coast airport.

Update: Bill Lindeke suggests: @trnsprttnst perhaps transportation scholars are inherently biased towards transporting things/people

Just as we have cut the earth into a grid of latitude and longitude (and knowing that each "block" of 1 degree latitude by 1 degree longitude gets smaller and smaller as we approach the poles), we similarly cut our cities and rural areas into a finer mesh from that same grid. Much of this arises from the various large scale ordinance surveys that took places in the Americas, Australia, and India. There are of course grids dating much earlier, to Miletus and Mohenjo Daro among many others. Not all grids are aligned with longitude and latitude, sometimes they align with local landscape features, but most of the modern ones are. (Where grids of different alignments come together, interesting spaces are created). Not all grids are squares, most are more like rectangles.

So why should we have 90-degree rectilinear grids?

The arguments in favor are that it:

1. simplifies construction and makes it easier to maximize the use of space in buildings,
2. simplifies real estate by making the life of the surveyor easier,
3. simplifies intersection management by reducing conflicts compared to a 6-way intersection,
4. is embedded in existing property rights and so impossible to change.

We in the modern world need not be bound to the primitive tools of the early surveyor, the primitive signal timings of the 1920s traffic engineer, or the primitive construction techniques of early carpenters. And while for existing development we might be locked into existing property rights, for new developments that doesn't follow.

The arguments against the rectilinear include that it:

1. is among the least efficient way to connect places from a transportation perspective,
2. reduces opportunities for interesting architecture,
3. wastes developable space by overbuilding roads.

There are many designs for non-rectilinear street networks. Ben-Joseph and Gordon (2000) (Hexagonal Planning in Theory and Practice (Journal of Urban Design 5(3) pp.237-265)) summarize a number of the 19th and 20th century designs. Most are simple aesthetic choices, as in Canberra, the planned capital city of Australia, and don't seem to relate to deeper urban organizational issues.

Rudolf Müller proposed The City of the Future: Hexagonal Building Concept for a New Division. Müller's plan offsets the 60-degree streets so that they come together in 4-way rather than 6-way intersections (though they are still at 60-degrees and not bent to make 90-degree intersections). This ensures that the cells in the plan are not bisected by roads, and that they are instead hexagonal blocks. This plan loses a lot of areas to ornamental parks in the middle of streets.

The circuity increase associated with a 90-degree rather than 60-degree network is obvious. Circuity (the ratio of Euclidean to Network distance) would be minimized if roads were at 0-degree angles. The downside is that this Euclidean network where everyone traveled in a straight-line would literally "pave the earth". Leaving aside the downsides for the environment of being so-paved, the more critical trade-off from a transportation perspective is construction costs. More roads are more expensive. So a network design trades-off travel costs accruing over time with the up-front construction and long-term maintenance costs. The optimal network design depends on the land use pattern it aims to serve. (And the land use pattern depends on the network design.) The City of Alonso or Von Thünen, with all jobs downtown merely requires a simple radial network to connect it. A polycentric or fully dispersed (homogeneous) city with everything spread uniformly across space begs for more cross-connections.

Charles Lamb's City Plan has the streets hexsect the hexagonal cells. In this case, the blocks are really triangles.

There is a large literature on the network design problem. One useful paper: Pierre Melut and Patrick O'Sullivan (1974) A Comparison of Simple Lattice Transport Networks for a Uniform Plain, Geographical Analysis 6(2) pp. 163–173, says:

The objective is to compare construction and transport costs for triangular [60-degree], orthogonal [90-degree], and hexagonal [120-degree] regular lattices as transport networks serving a uniform, unbounded plain. The lattices are standardized so that the average distance from the elementary area to the edge is the same for each. This standardization results in equal construction costs for the three networks; thus, the comparison can be made in terms of route factors [circuity], which favors the triangular lattice over the other two.

Because the circuitous network is less efficient, more network pavement and track and vehicle mileage must be provided to enable the same amount of transportation. This wastes spaces that could be better allocated to non-transportation purposes.

The lattice itself comprises a single level in a hierarchical system. Selected links in a lattice can be reinforced to make them faster, attracting traffic. This process of reinforcement is natural with investment rules that favor more heavily trafficked routes and explains the hierarchy of roads. If it is based on simple reinforcement of existing links rather than creation of new links, that hierarchy will not affect the topology of the network.

Ask MetaFilter has an interesting thread on Comparing perimeters of arrays of hexagons vs. squares - geometry tiling resolved . A key point is that arranging hexagons into a square-like shape has a higher perimeter than arranging squares into a square-like shape.

 __    __    __    __    __
/  \__/  \__/  \__/  \__/  \
\__/  \__/  \__/  \__/  \__/
/  \__/  \__/  \__/  \__/  \
\__/  \__/  \__/  \__/  \__/
/  \__/  \__/  \__/  \__/  \
\__/  \__/  \__/  \__/  \__/
/  \__/  \__/  \__/  \__/  \
\__/  \__/  \__/  \__/  \__/
/  \__/  \__/  \__/  \__/  \
\__/  \__/  \__/  \__/  \__/
  Diagram 1. Sample hex map

Jellicle wrote:

I think your problem is this - to minimize the perimeter of n hexagons, when you add each new hexagon to the previously-existing group, you have to add it in such a way that touches the most neighbors possible. You would never add a hexagon that touches only on one face if you could add it somewhere else where it touches two faces or three faces, right? If you look at diagram 1 here (which is hexes in a grid shape), you see several hexes at the four corners which touch only on two faces, while there are areas on the outer surface at the top and bottom where those hexes could be placed where they would touch on three faces instead of two. So simply moving those four corner hexes would reduce the perimeter without changing the surface area.

Yet we know the hexagon is efficient, it replicates the closest packing of circles. (Take a penny, surround it with pennies so that they are all tangent. The central penny touches six others.) Thus following the closest-packing argument, the hexagon as geometrical shape is not sufficient for efficiency, we must also arrange those shapes into an efficient pattern, in this case, something more like the Glinski Chess Board:

Much of the inspiration for thinking about hex-maps comes from the gaming community, where such maps have been used since the 1961, when a Hex map was used for the Avalon Hill game Gettysburg. It has since become a standard that is widely used to represent directions of movement in games.

So, although we talk about "grids" as being necessary for connectivity, we can get even more connectivity if we think about a variety of different geometries. It would be a shame if we got locked into grid geometries for new developments when there are so many alternatives to be had.

I am on the program committee for the ICA Workshop on Street Networks and Transport:

"Street networks, as one of the oldest infrastructure of transport in the world, play a significant role in modernization, sustainable development, and human daily activities in both ancient and modern times. Although street networks have been well studied in a variety of engineering and scientific disciplines including for instance transport, geography, urban planning, economics and even physics, our understanding of street networks in terms of their structure and dynamics is still very limited to deal with real world problems such as traffic jams, pollution, and human evacuations in case of disaster management. Thanks to the rapid development of geographic information science and related technologies, abundant data of street networks have been collected for better understanding the networks’ behavior, and human activities constrained by the networks. This ICA workshop is intended to gather researchers together to present the state of the art research and studies, in an interdisciplinary setting, on street networks and transport. Suggested topics include, but not limited to as long as they address issues related to street networks and/or transport:

• Spatial statistics and spatial analysis along networks
• Topological analysis and space syntax
• Pattern recognition with street networks
• Map generalization on street networks Complexity measurement of street networks
• Human evacuations and simulations
• Transport modeling based on street networks
• Geospatial analysis of the OpenStreetMap data

Submission

All manuscripts in a length of 6000-7000 words should be in English, single column, single-spaced with figures and tables within the text. The manuscripts in MS Word 2003 format should contain authors’ affiliation and email, abstract (no longer than 200 words), and up to five keywords. To submit, please use EasyChair at http://www.easychair.org/conferences/?conf=icaworkshop2013
"

Now @ Streets.MN : In praise of contiguity :

"After seeing other places throughout the world, notably Toronto, London, Manhattan, any continental European city, even Washington DC, I believe the problem with making Minneapolis a first rate pedestrian city is the lack of contiguity. There are some really good walkable sections, but they are not connected well (or at all)."

WALKABLE Dallas-Fort Worth: Why Grids Matter and We Should Recreate Them At All Cost (Strictly for the ROI):

"A dendritic system is defined by a branching structure that funnels movement in one direction. Whereas a conventional grid provides a multiplicity of routes. The key defining factor is choice. Think about this from where you live and you're on your way to work or to pick up the kids or to get a gallon of milk. How many routes can you take? What if there is a wreck along the way? How many different modes of travel are quick and convenient?

There is quite a bit of talk about the emergent nature of cities as complex systems, but few really understand the applicability to how we design our cities and the dynamics of the process. What we have to understand is that emergence implies a second level of organization that is largely beyond our control. Why? Because we can only 'design' the first level of organization, whether it is a building or a road. Because designers are only one person or group working on one problem. The second order of 'design' happens when everybody else decides how to use the system. That can't be designed en masse, only nudged in certain directions depending upon how well we understand the dynamics of this emergence."

If anyone was wondering why Google is interested in self-driving vehicles ... imagine the future as robot black cabs. The Next Web: London’s black cabs to get free high-speed WiFi hotspots from early 2013

Mary Meeker's annual Internet Trends slideshow: 2012 KPCB Internet Trends Year-End Update

Nice slides on Asset-Heavy vs. Asset-Light dealing with transportation.

Some Sandy links:

(1) Subway Recovery:

In general I am really impressed with the speed of the subway recovery. If periodic flooding does not destroy the network, maybe New York does not need to relocate or build really expensive defenses, just take a 1 or 2 week vacation every hurricane.

From WNYC: Subway Network Recovery animation

From NYT: New York Subways Find Magic in Speedy Hurricane Recovery

(2) Gas Rationing:

From NYT: In New York Gas Shortage, Missed Opportunities and Miscalculations

From NYT: Odd-Even License Plate Rules Have a History

We really need to invent/deploy gasoline-powered gas stations and refineries. It seems many stations had gas they could not pump for lack of electricity. Obviously lots of other problems as well, and I am sure there are risks of sparking near lots of gasoline, but this should be a solvable problem.

David J. Giacomin, Luke S. James, and David M. Levinson (2012) Trends in Metropolitan Network Circuity. (Working Paper)

Because people seek to minimize their time and travel distance (or cost) when commuting, the circuity–the ratio of network distance traveled to the Euclidean distance between two points–plays an intricate role in the metropolitan economy. This paper seeks to measure the circuity of the United States’ 51 most populated Metropolitan Statistical Areas and identify trends in those circuities over the time period from 1990- 2010. With many factors playing a role such as suburban development and varying economic trends in metropolitan areas over this timeframe, much is to consider when calculating results. In general, circuity is increasing over time.

A new paper by David Eichler, Hillel Bar-Gera and Meir Blachman in Networks and Spatial Economics describing perhaps the strangest street network you will see (sadly behind a paywall):

Vortex-Based Zero-Conflict Design of Urban Road Networks : "A novel approach is suggested for reducing traffic conflicts in at-grade (2D) urban networks. Intersections without primary vehicular conflicts are defined as zero traffic conflict (ZTC) designs. A complete classification of maximal ZTC designs is presented, including designs that combine driving on the right side in some streets and driving on the left side in other streets. It is shown that there are 9 four-way and 3 three-way maximal ZTC intersection designs, to within mirror, rotation, and arrow reversal symmetry. Vortices are used to design networks where all or most intersections are ZTC. Increases in average travel distance, relative to unrestricted intersecting flow, are explicitly calculated for grid-networks of sizes 10 by 10, 10 by 20 and 20 by 20 nodes with evenly distributed origins and destinations. The exact increases depend primarily on various short-range conditions, such as the access to the network. The average distance increase in most cases examined is up to four blocks. These results suggest that there is a potential for the new designs to be relevant candidates in certain circumstances, and that further study of them is worthwhile."

Vortices are of course in a sense just giant roundabouts. The Magic Roundabout of Swindon is the most complex I know of. This can also be seen in parts in neighborhood traffic calming districts. The unrestricted intersections could become roundabouts to avoid conflicts.

Note: Route factor = what we call Circuity, I think the authors overestimate the additional distance traveled, since people will orient their trips to the network.

From February: GTI/UTC Lunchtime Lecture Series - Dr. David Levinson - YouTube: "Network Structure and Travel Behavior"

Abstract: Transportation networks have an underlying structure, defined by the layout, arrangement and the connectivity of the individual network elements, namely the road segments and their intersections. The differences in network structure exist among and between networks. This presentation argues that travellers perceive and respond to these differences in underlying network structure and complexity, resulting in differences in observed travel patterns. This hypothesized relationship between network structure and travel is analyzed using individual and aggregate level travel and network data from metropolitan regions across the U.S. Various measures of network structure, compiled from existing sources, are used to quantify the structure of street networks. The relation between these quantitative measures and travel is then identified using econometric models.

Newly posted @streets.mn: The Missing Link

Akamai: State of the Internet Report [Comment: It's not faster than last year, because, like roads, it is not rationed or priced properly]

Tim Lee @ Ars: Why bandwidth caps could be a threat to competition: "Since the first dot-com boom, unmetered Internet access has been the industry standard. But recently, usage-based billing has been staging a comeback. Comcast instituted a bandwidth cap in 2008, and some other wired ISPs, including AT&T, have followed suit. In 2010, three of the four national wireless carriers—Sprint is the only holdout—switched from unlimited data plans to plans featuring bandwidth caps."

Tom Vanderbilt @ The Wilson Quarterly: The Call of the Future : "Today we worry about the social effects of the Internet. A century ago, it was the telephone that threatened to reinvent society." ["He is currently at work on You May Also Like, a book about the mysteries of human preferences."]

David Willetts @ The Guardian: The UK government is promising: Open, free access to academic research [Woot!]

Jacoba Urist @ The Atlantic No Taxes, No Travel: Why the IRS Wants the Right to Seize Your Passport:

"It all started last fall, when Senator Barbara Boxer introduced the "Moving Ahead for Progress in the 21st Century Act" (or "MAP-21" as it's now called), to reauthorize funds for federal highway and transportation programs. While that doesn't sound like anything having to do with your taxes, the bill includes a little-noticed section that allows the State Department to "deny, revoke or limit" passport rights for any taxpayers with "serious delinquencies."

Here's how it would work. If someone owed more than $50,000 in back taxes, the IRS would be able to send their name over to the passport office for suspension, provided that the IRS already either filed a public lien or a assessed a levy for the outstanding balance. The bill does provide a few exceptions though. For example, if a person has set up a payment plan (that they're paying in a timely manner), is legitimately disputing the debt, or has an emergency situation or humanitarian reason and must travel internationally, they may be able to leave for a limited time despite their unpaid taxes."

Stephen Levy @ Wired: Going With the Flow: Google's Secret Switch to the Next Wave of Networking:

"If any company has potential to change the networking game, it is Google. The company has essentially two huge networks: the one that connects users to Google services (Search, Gmail, YouTube, etc.) and another that connects Google data centers to each other. It makes sense to bifurcate the information that way because the data flow in each case has different characteristics and demand. The user network has a smooth flow, generally adopting a diurnal pattern as users in a geographic region work and sleep. The performance of the user network also has higher standards, as users will get impatient (or leave!) if services are slow. In the user-facing network you also need every packet to arrive intact — customers would be pretty unhappy if a key sentence in a document or e-mail was dropped.

The internal backbone, in contrast, has wild swings in demand — it is “bursty” rather than steady. Google is in control of scheduling internal traffic, but it faces difficulties in traffic engineering. Often Google has to move many petabytes of data (indexes of the entire web, millions of backup copies of user Gmail) from one place to another. When Google updates or creates a new service, it wants it available worldwide in a timely fashion — and it wants to be able to predict accurately how quickly the process will take.

“There’s a lot of data center to data center traffic that has different business priorities,” says Stephen Stuart, a Google distinguished engineer who specializes in infrastructure. “Figuring out the right thing to move out of the way so that more important traffic could go through was a challenge.”

But Google found an answer in OpenFlow, an open source system jointly devised by scientists at Stanford and the University of California at Berkeley. Adopting an approach known as Software Defined Networking (SDN), OpenFlow gives network operators a dramatically increased level of control by separating the two functions of networking equipment: packet switching and management. OpenFlow moves the control functions to servers, allowing for more complexity, efficiency and flexibility."

Reuben Collins @ Streets.mn The Problem of Hiawatha Avenue

Recently published: Levinson D, Huang A, 2012, "A positive theory of network connectivity" Environment and Planning B: Planning and Design 39(2) 308 – 325. [doi:10.1068/b37094]

Abstract. In this paper we develop a positive theory of network connectivity, seeking to provide the microfoundations of alternative network topologies as the result of self-interested actors. By building roads, landowners hope to increase their parcels’ accessibility and economic value. A simulation model is performed on a grid-like land-use layer with a downtown in the center. The degree to which the networks are tree-like is evaluated. This research posits that road networks experience an evolutionary process where a tree-like structure first emerges around the centered parcel before the network pushes outward to the periphery. Road network topology becomes increasingly connected as the accessibility value of reaching other parcels increases. The results demonstrate that, even without a centralized authority, road networks can display the property of self-organization and evolution, and that, in the absence of intervention, the degree to which a network structure is tree-like or web-like results from the underlying economies.

Keywords: road network, network growth, network structure, treeness, circuitness, topology

Download Older Preprint.

Jessica Schoner just received an honorable mention from APA's Transportation Planning Division for her paper (which was a class term paper (technically 2 term papers), not a thesis or dissertation!): Shifting Gears: A cross-regional analysis of bicycle facility networks and ridership. A Reviewer said: "Of all the years doing this contest this is by far the best on bicycling I've seen." If you care about network structure, or about travel behavior, or about bicycles, read it.

Robert Bruegmann @ Bloomberg: Driverless Car Could Defy Sprawl Rules:

"The driverless car could well extend that flexibility in dramatic fashion, combining some characteristics of automobiles and public transportation and allowing people more choice in the way they live, whether it involves more compact, high-density cities, more dispersed low-density settlements -- call it sprawl if you like -- or, perhaps most likely, all of the above."

Fanis Grammenos @ Planetizen Choosing a Grid, or Not :

"Breaking the convenient, but outdated, uniformity of the 18th and 19th Century American grids would be a first step in recovering the land efficiency mandated by current ecological and economic imperatives. Pointing in that direction, Savannah’s composite, cellular grid includes variable size streets and blocks for private, civic and religious functions. A second step would be to include block sizes that can accommodate building types and sizes unknown in the 1800s, again defying block uniformity. A third step would be to adapt its streets for the now universal motorized mobility, of cars, buses, trucks, trams and motorcycles, that is radically different from when oxen, equine and legs shared the transport of goods and people."

Eric Jaffe @ Atlantic Cities: The Tale of a Taxi Driver Who Just Won't Stop Driving [He claims he is not a taxi driver, since he doesn't charge (making it up in tips), the court disagreed]

Lynne Kiesling @ Knowledge Problem: Extreme Makeover: Regulation Edition :

"Yes. Hayek’s Pretence of Knowledge meets Smith’s “man of system”, Tullock’s rent seeking, and Olson’s concentrated benefits and diffuse costs. Regulatory complexity creates benefits for politically-powerful special interests, but it creates costs for everyone else, and this ongoing process feeds the egos of our elected representatives who believe they can engineer, design, and manipulate society to achieve their desired outcomes."

Capital Business Blog - The Washington Post: In White Flint, the mall is being turned into a town :

"The plans ultimately call for 5.2 million square feet of buildings, including 1 million square feet offices in three buildings along Rockville Pike, 1 million square feet of retail, 2,500 residential units and a 300-room hotel. The current three-level mall is about 800,000 square feet.

Civic amenities are also envisioned. On the south side of the property the companies have reserved space for the construction of a new elementary school and on the east side plan to build a public park, part of 13.1 acres of open space on the property."

CBC News: TTC chief Gary Webster fired:

"TTC chief general manager Gary Webster has been relieved of his duties, following a vote during a special meeting of transit commissioners Tuesday.

In a motion describing termination "without just cause," the transit commission voted 5-4 to fire Webster, who has worked at the service for 35 years, just two weeks after he expressed open defiance to a subway plan championed by Mayor Rob Ford. His ouster comes a year before he was set to retire.

"This was not how I expected this to end — certainly not how I wanted it to end," Webster told reporters shortly after his termination. "But clearly the choice has been made to replace me as chief general manager and I accept that.""

Joe Soucheray @ Twincities.com: Let's turn I-94 into a tollway. No, I'm serious.:

"About 30 minutes after you cross the Illinois border below Milwaukee, you are offered the tollway option, which is the only way to go. I went last weekend, and before I left, the CP slapped the transponder onto my windshield.

It made me feel big city. I am certain that if I lived in the western suburbs or had to use I-35W, I'd be a MnPASS customer."

The Transportationist is now also syndicated on Alltop

I posted an article on County Seats at streets.mn

Recently published:

• Parthasarathi, Pavithra, Hartwig Hochmair, and David Levinson (2012) Network Structure and Spatial Separation. Environment and Planning B: Planning and Design 39(1) 137-154 [download]

Abstract. This research aims to identify the role of network architecture in influencing individual travel behavior using travel survey data from Minneapolis-Saint Paul and Florida (Fort Lauderdale and Miami). Various measures of network structure, compiled from existing sources, are used to quantify roadway networks, and to capture the arrangement and connectivity of nodes and links in the networks and the spatial variations that exist among and within networks. The regression models show that travel behavior is correlated with network design.

Keywords: network structure, travel behavior

Recently published: Levinson, David (2011) Network Structure and City Size. PLoS One PLoS ONE 7(1): e29721, January 12, 2012 [doi]

Network structure varies across cities. This variation may yield important knowledge about how the internal structure of the city affects its performance. This paper systematically compares a set of surface transportation network structure variables (connectivity, hierarchy, circuity, treeness, entropy, accessibility) across the 50 largest metropolitan areas in the United States. A set of scaling parameters are discovered to show how network size and structure vary with city size. These results suggest that larger cities are physically more inter-connected. Hypotheses are presented as to why this might obtain. This paper then consistently measures and ranks access to jobs across 50 US metropolitan areas. It uses that accessibility measure, along with network structure variables and city size to help explain journey-to-work time and auto mode share in those cities. A 1 percent increase in accessibility reduces average metropolitan commute times by about 90 seconds each way. A 1 percent increase in network connectivity reduces commute time by 0.1 percent. A 1 percent increase in accessibility results in a 0.0575 percent drop in auto mode share, while a 1 percent increase in treeness reduces auto mode share by 0.061 percent. Use of accessibility and network structure measures is important for planning and evaluating the performance of network investments and land use changes. Keywords: Connectivity, Network Structure, Transportation Geography, Network Science, City Size, Scaling Rules, Accessibility, Travel Behavior, Mode Share, Journey-to-Work

This paper has several features:

1. The paper includes a ranking of 50 US cities by estimated accessibility (Table 3). This estimate is macroscopic, though I think quite plausible, and shows the variation in the 10 minute vs. 20 minute ... vs. 60 minute and composite accessibilities. The composite numbers are more or less what you expect, but some small cities are quite fast, so have high 10 or 20 minute accessibilities by car. Lots of work remains to be done on this (both multiple modes and multiple points in time) but this should be a valuable metric.
2. Larger cities are better connected. They are also more productive. This research suggests a hypothesis (which further research will need to test) that variations in network structure may explain variations of economic output. More connected cities are more efficient. It is not simply how many people are in the city (the classic economy of agglomeration argument) but how they are connected that affects their productivity.

I will also comment about the publication itself. It was published in PLoS One, a first for me. PLoS ONE is a newish, open content journal across part of the Public Library of Science family that aims to represent all fields of study. I did this as an experiment as much as anything. The paper is out less than 4 months after submission, and 2 months after revision. This is *fast*, much faster than for-profit publishers offer. The journal is interdisciplinary, and does not winnow for importance (letting the field do that), instead winnowing for quality of the work and its description. Everyone in the field knows how arbitrary publication is when paper is a constraint. This seems an improvement.

BBC News: - Driverless car: Google awarded US patent for technology

USA Today: Swedish automaker Saab files for bankruptcy

StarTribune: Planned Internet gateway could provide backup [Network redundancy is good]

Ars Technica Reports: Data caps a "crude and unfair tool" for easing online congestion: "Internet providers argue that they need to impose monthly data caps on their users in order to slay the "bandwidth hogs" running wild and free through their networks, goring ordinary users with their tusks when all those users want to do is view some funny cat pictures online after a tough day at the office. The idea is that a monthly quota can reduce the amount of network congestion during peak hours throughout the month. Fact or fiction?"

This is like limiting car ownership to reduce congestion, or imposing a gas tax. Sure it works in the crudest sense, but it is an atomic bomb where a precision bullet (congestion pricing or peak period quotas) would do.

Recently published: Carrion-Madera, Carlos, David Levinson, and Kathleen Harder (2011) Value of Travel-Time Reliability: Commuters' Route-Choice Behavior in the Twin Cities (OTREC-RR-11-21):

"Travel-time variability is a noteworthy factor in network performance. It measures the temporal uncertainty experienced by users in their movement between any two nodes in a network. The importance of the time variance depends on the penalties incurred by the users. In road networks, travelers consider the existence of this journey uncertainty in their selection of routes. This choice process takes into account travel-time variability and other characteristics of the travelers and the road network. In this complex behavioral response, a feasible decision is spawned based on not only the amalgamation of attributes, but also on the experience travelers incurred from previous situations. Over the past several years, the analysis of these behavioral responses (travelers’ route choices) to fluctuations in travel-time variability has become a central topic in transportation research. These have generally been based on theoretical approaches built upon Wardropian equilibrium, or empirical formulations using Random Utility Theory. This report focuses on the travel behavior of commuters using Interstate 394 (I-394) and the swapping (bridge) choice behavior of commuters crossing the Mississippi River in Minneapolis. The inferences of this report are based on collected Global Positioning System (GPS) tracking data and accompanying surveys. Furthermore, it also employs two distinct approaches (estimation of Value of Reliability [VOR] and econometric modeling with travelers’ intrapersonal data) in order to analyze the behavioral responses of two distinct sets of subjects in the Minneapolis-Saint Paul (Twin Cities) area."

Posted: Visualizing US expansion through post offices. from Derek Watkins on Vimeo.

Remember all that talk about the "Death of Distance". Well it turns out even in the supposedly distance-free internet wholesale market, distance still matters and is being suggested as a price differentiator. Connected Planet writes about: The return of distance-based pricing (for wholesale ISPs)? :

"Using just three or four service tiers could improve a wholesale ISP’s profit substantially, the researchers argue in a paper to be presented at the SIGCOMM conference in Toronto today.

The paper titled “How Many Tiers? Pricing in the Internet Transit Market” is based on data collected using a model developed by the research team. The researchers say their creation is the first economic model that takes real traffic data as an input to understand the impact of tiered, destination-based pricing on an ISP’s profit."

Obviously market differentiation and stratification is important, with more differentiators allowing producers to capture more value (and consumers less). And obviously the number of links that are traversed is associated with the underlying cost of infrastructure. The only question is whether the increased transaction costs outweigh the profits.

The analyst Horace Dediu writes in Harvard Business Review: Google's Strategic Mistakes Drove Motorola Buy:

It's an innovative, if not convoluted, business model: Building and giving away the plumbing so that homes are granted unhindered access to free Google utility services (whose meter readings are sold to the highest bidder). But it comes with more complications. … Instead, with Motorola, Google got a hold of the vehicle through which it can create and sell integrated products. The company is thus no longer just a plumber but also a house builder and real estate developer. It can now build showcases that demonstrate the value of its services. The challenge then is how it will sell plumbing to contractors while it also competes with them by building houses. Android's big bet has yet to pay off and Google just doubled down.

This is a really interesting metaphor. Replace plumbing with roads, Google with transportation agencies, and Motorola with land development, and you have the model of Land Value Capture we have been talking about. Like Google giving away the OS plumbing and make it back in advertising, states give away roads and transit lines to users, hoping to make it back (somehow) in tax revenue (maybe?). Google, following Apple's lead, has decided it needs to internalize the value chain to avoid the convolutedness of the market model they had created, which gave them large share, but few profits in mobile. We need to come to the same realization in transportation, in favor of more direct vertical integration of transportation and land use.

Working paper:

• Zhu, Shanjiang and David Levinson (2010), Do people use the shortest path? An empirical test of Wardrop’s first principle. Presented at 4th International Symposium on Transportation Network Reliability, July 2010, Minneapolis, MN.

Most recent route choice models, following either the random utility maximization or rule-based paradigm, require explicit enumeration of feasible routes. The quality of model estimation and prediction is sensitive to the appropriateness of the consideration set. However, few empirical studies of revealed route characteristics have been reported in the literature. This study evaluates widely applied shortest path assumption by evaluating morning commute routes followed by residents of the Minneapolis - St. Paul metropolitan area. Accurate GPS and GIS data were employed to reveal routes people used over an eight to thirteen week period. Most people do not choose the shortest path. Using three weeks of that data, we find that current route choice set generation algorithms do not reveal the majority of paths that individuals took. Findings from this study may provide guidance for future efforts in building better route choice models.

JEL-Code: R41, R48, D63

Keywords: Transportation planning, route choice, travel behavior, link performance

• Levinson, David (2011) Network Structure and City Size. (working paper)

Network structure varies across cities. This variation may yield important knowledge about how the internal structure of the city affects its performance. This paper systematically compares a set of surface transportation network structure variables (connectivity, hierarchy, circuity, treeness, entropy, accessibility) across the 50 largest metropolitan areas in the United States. It finds most of these measures vary with city size. A set of scaling parameters are discovered to show how network size and structure vary with city size. These results suggest that larger cities are physically more inter-connected.

Keywords: Connectivity, Network Structure, Transportation Geography, Network Science, City Size, Scaling Rules

Urbagram: Geodesic"A geodesic, the shortest path between two points in a mathematical space. Early urban cybernetic interfaces imparted this machine intelligence to citizens via origin-destination matrices placed at public transport nodes, introducing graph theoretic concepts to the urban masses. This TfL Journey Planner (1963) consists of separate origin and destination button matrices with a CRT monitor in the center. The machine communicates the shortest path between any two selected nodes."

There is as far as I know one transportation test network archive, sponsored by Hillel Bar-Gera. We have put a set of 16 test networks up at the

Nexus website. The networks used in Table 5 of Xie and Levinson (2007) Measuring the Structure of Road Networks are simple ASCII node and link tables.

Enjoy.