Category Archives: Urban Systems

Traffic Jams Make Cities Splinter into Subcenters: A rule of urban expansion could guide smarter growth – SciAm

I get quoted by Sarah Fecht in Scientific American (310(2)):

Most of the world’s cities started from an important marketplace or town square. Over time, they developed multiple centers where people could work, shop and play. But why? Some economists have suggested that cities fragment because of agglomeration—businesses that spring up in clusters increase their chances of success.

Yet physicists have arrived at a slightly different explanation: traffic jams. Marc Barthelemy and Rémi Louf, both at the Institute of Theoretical Physics in France, designed a mathematical model to explain how cities and their surrounding suburbs evolve. Their research suggests that as a city grows and congested roadways make it increasingly difficult to get to the center, subcenters emerge along the outskirts. “It’s an interplay between how attractive the place is and how much time it takes to go there,” Barthelemy says. Cities with accommodating transportation networks remain centralized longer, he adds.

The physicists validated their ideas using data from 9,000 U.S. cities and towns of different sizes.

A better understanding of how metropolitan areas evolve could prove useful, considering that two thirds of the world’s population is expected to live in urban areas by 2050, notes David Levinson, a transportation engineer at the University of Minnesota. “There’s a lot of urbanization left to happen,” Levinson says. “If planners imagine a city to take a particular form, but that’s not the way the city wants to behave, we’ll be making unwise investments.”

Barthelemy believes the model could also come in handy for estimating traffic delays, gas consumption and carbon dioxide emissions. “I think that this opens up the path to some really quantitative insights about cities,” he says. “We can take simple mechanisms, simple ingredients, and in the end predict how important properties are scaling with population.”

This article was originally published with the title “The Traffic Effect.”

Peer-to-peer car sharing gains momentum within rental car industry

I was interviewed by Catherine Boardman for the article Peer-to-peer car sharing gains momentum within rental car industry:

“Transportation analyst David Levinson said although traditional car-rental companies will not fade away, there is a niche for peer-to-peer services that can offer a quicker, easier alternative.

‘Apps can erode some of the hassle, and maybe today’s companies are too sclerotic to innovate,’ Levinson said.”

Accessibility and non-work destination choice: A microscopic analysis of GPS travel data


Congratulations to Dr. Arthur Huang for successfully completing and defending his dissertation: Accessibility and non-work destination choice: A microscopic analysis of GPS travel data

The advancements of GPS and GIS technologies provide new opportunities for investigating vehicle trip generation and destination choice at the microscopic level. This research models how land use and road network structure influence non-work, non-home vehicle trip generation and non-work destination choice in the context of trip chains, using the in-vehicle GPS travel data in the Minneapolis-St. Paul Metropolitan Area. This research includes three key parts: modeling non-work vehicle trip generation, modeling non-work, single-destination choice, and modeling non-work, two-destination choice. This research contributes to methodologies in modeling single-destination choice and multiple-destination choice and tests several hypotheses which were not investigated before.

In modeling non-work vehicle trip generation, this research identifies correlation of trips made by the same individual in the trip generation models. To control for this effect, five mixed-effects models are systematically applied: mixed-effects linear model, mixed-effects log-linear model, mixed-effects negative binomial model, and mixed-effects ordered logistic model. The mixed-effects ordered logistic model produces the highest goodness of fit for our data and therefore is recommended.

In modeling non-work, single-destination choice, this research proposes a new method to build choice sets which combines survival analysis and random sampling. A systematic comparison of the goodness of fit of models with various choice set sizes is also performed to determine an appropriate choice set size. In modeling non-work, multiple-destination choice, this research proposes and compare three new approaches to build choice sets for two-destination choice in the context of trip chains. The outcomes of these approaches are empirically compared and we recommend the major/minor-destination approach for modeling two-destination choice. The modeling procedure can be expanded to trip chains with more than two destinations.

Our empirical findings reveal that:

  1. Although accessibility around home is not found to have statistically significant effects on non-work vehicle trips, the diversity of services within 10 to 15 minutes and 15 and 20 minutes from home can help reduce the number of non-work vehicle trips.
  2. Accessibility and diversity of services at destinations influence destination choice but they do not exert the same level of impact. The major destination in a trip chain tends to influence the decision more than the minor destination.
  3. The more dissimilar the two destinations in a trip chain are, the more attractive the trip chain is.
  4. Route-specific network measures such as turn index, speed discontinuity, axis of travel, and trip chains’ travel time saving ratio display statistically significant effects on destination choice.
    Our findings have implications on transportation planning for creating flourishing retail clusters and reducing the amount of vehicle travel.

After working at Valparaiso University last year, he is currently teaching at the University of Minnesota Duluth.

Urban amusement parks |


Cross-posted at  Urban amusement parks:

“All the cool cities have urban amusement parks. In fact Minneapolis-St. Paul is the largest urban agglomeration in the upper Midwest without an urban amusement park.”

Urban amusement parks

Next to the originator of a good sentence is the first quoter of it” – Ralph Waldo Emerson Quotation and Originality 

Good artists copy, great artists steal.” – Pablo Picasso (attributed but unsourced)

One of the surest tests [of the superiority or inferiority of a poet] is the way in which a poet borrows. Immature poets imitate; mature poets steal; bad poets deface what they take, and good poets make it into something better, or at least something different. The good poet welds his theft into a whole of feeling which is unique, utterly different than that from which it is torn; the bad poet throws it into something which has no cohesion. A good poet will usually borrow from authors remote in time, or alien in language, or diverse in interest.” – Eliot, T.S., “Philip Massinger,” The Sacred Wood, New York:, 2000.

Good cities copy, great cities steal.” — Anonymous on Streets.MN

All the cool cities have urban amusement parks. In fact Minneapolis-St. Paul is the largest urban agglomeration in the upper Midwest without an urban amusement park.

Oh, you say, but the Greater MSP metropolis has ValleyfairNickelodeon Universe at theMall of America, the Midway and the Kidway at the State Fair, Comotown, and, coming soon, a Ferris Wheel at the old Psycho Suzi’s.

Valleyfair is suburban, the Midway and Kidway are seasonal, Como Town is in a large park fairly remote from the urban core, and the Mall of America, is, well, the Mall of America (though to be fair, it is more easily accessible by mass transit than anything but the State Fair).

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The history of Minneapolis and St. Paul includes many amusement areas that are no longer with us, including parks in Excelsior and Big Island on Lake Minnetonka, the short-livedWonderland in Longfellow, and Wildwood on White Bear Lake (Wildwood and Big Island were both owned by Twin City Rapid Transit as a way of better utilizing transit capacity).

Tivoli Gardens

What I am referring to are places like Chicago’s Navy Pier, Sydney’s Luna Park, the London Eye, or the best I have seen, Copenhagen’s Tivoli Gardens. They are walkable from the urban core or easily accessed by transit, and thus at least as geared to tourists as to residents. Tivoli and Navy Pier are fully programmed, so in addition to rides, there are numerous events so the sites are occupied day and evening much of the year. While Navy Pier has the scenery of Lake Michigan, Tivoli has no special natural advantage and is largely inward looking. Tivoli attracts about 4 million visitors per year. It is adjacent to a major railway station, helping attract visitors. My Tivoli photos can be seen on Flickr.

London Eye

View Map of Tivoli Gardens, Copenhagen


The site I have in mind is near Saint Anthony Main. This includes both vacant lots and industrial parcels that will eventually be reconfigured. We can start with the huge parking lot at 2nd Avenue and 2nd Street (and across the old Pillsbury Technology Center parking lot as well). I realize Metal-Matic is currently occupied by a business that employs people, but industrial sites in the city clearly have their days numbered as the value of land for other uses outweighs their use in manufacturing. We should be thinking about what comes next (without actually forcing them out). The site is adjacent to the freeway and the University, creating some built-in demand, as well as a short walk or NiceRide across the Stone Arch Bridge from downtown, catering to both the business and tourist crowd. These sites could become another 6-story stick frame apartment building, but it could be something more memorable.

Sydney - Darling Harbour Carousel

The land under the freeway could also be repurposed as part of this endeavor. There are lots of examples.

View Map of St. Anthony Main area

There are many other good sites, please identify some in the comments. The Metrodome would have been one, but it is to be reconfigured as something else.


I am trying to speak in a language public officials will understand. This does not imply an endorsement of this funding mechanism.

This lack of an urban amusement park constitutes a travesty that should be rectified with a TIF-financed economic development program as soon as possible. It has been shown bynumerous studies that urban amusement parks result in people spending money, which any macro-economist worth his salt-water will say is good for the economy.

OK, end of sarcasm. This doesn’t need to be a public facility. If it is popular, it should be able to pay for itself, like the State Fair. What it needs is to be enabled.



This is of course just speculation, a Fantasy-land so to speak. But with some vision, the cities should be able to attract an amusement park builder to create an attraction (or if Minneapolis gets one, St. Paul will want one too, so make that two attractions) that appeal(s) to the masses more than 8 nights a year.


Path dependence

If you don’t know where you’re going, any path will get you there.

Path dependence is the idea that where we are today depends critically on where we were yesterday. Some systems are path independent, those that have a single unique equilibrium. Finding the solutions to some math problems is independent of where you start, as long as you follow a particular algorithm.

However, most systems we deal with on a daily basis have some characteristics of path dependence. Where you live might depend on what job you took, which depends on what your previous job was and where you went to school, and a different decision anywhere along the way would change today’s position.

Nowhere is this more true than transportation. On the one hand, it is obvious that certain locations were destined to be important cities because of significant natural advantages. New York has a deep harbor at the confluence of major navigable river. Chicago is at the pivot point between vast agricultural lands to the Northwest and the shortest land path to the East Coast. It was natural railroads would flow through the point on the map we now call Chicago.

On the other hand, many city sites that were selected for natural advantages in one technological era (The Romans selected London and the Dutch and English chose New York in large part for their capability as ports), remain important even after that technology becomes obsolete. With the logistics revolution and the new dominance of container shipping, London’s shipping has moved northeast to Felixstowe as large container ships cannot easily ply the Thames, while New York’s shipping has migrated to the wide open spaces of New Jersey.

The one-time advantages result in a set of complementary investments and inter-related decisions that take on a life of their own. Because of local trading advantages, commodities markets, banks, insurers, and other related organizations located nearby. A critical mass of those institutions felt no need to migrate just because their initial raison d’être vanished. While a building is under construction, temporary framing will often be used until the more permanent structure is erected. Once the final building can stand on its own, the falsework is dismantled. In a sense, everything is falsework for what comes after.

This kind of mutual complementarity happens repeatedly in transportation. Airplanes are the perfect example of mobile capital. If Amalgamated Airlines no longer wants to serve a particular city pair, the airplane can easily be redeployed elsewhere. Yet 80 years into the commercial aviation industry, airlines today serve mostly the same hubs their predecessors did on the Airmail routes of the 1930s. American Airlines is still in Dallas, United in Chicago, Delta (Northwest) in Minneapolis, and so on.

While very few decisions are completely irreversible, transportation decisions come close. Where we place a right-of-way, or an airport will explain where that facility will be decades, or even centuries from now.

A slight deviation from the efficient path to solve a short term problem today will cost travelers time for years to come. It is important to get the design right for the long term. (Undoubtedly this has social costs, see e.g. I-94 through the Rondo in Saint Paul).

But a slight deviation from the path will also change what the long term is. Build a bridge “here” rather than “there”, and then you will adjust all of the roads feeding into the bridge to meet it “here” (instead of “there”). And then land will be developed along the road to “here” to take advantage of the newly created accessibility, properties will be platted, buildings will be built, travel and trade patterns established, and other critical dependencies will come to assume that the bridge is “here”. At some point, say 50 years in the future, the bridge will need to be replaced. Even if “there” was a better location than “here” initially, after five decades of adaptation, it is quite likely that “here” is better now. The whole may have been better were a different initial decision been made, given conditions at the time. Given current realities, that path must now be foregone.

In transportation we say build it right the first time, because there won’t be a second chance. And that is true. But also remember the world will adapt to whatever we do, and we cannot let the perfect be the enemy of the good.

Evaluating Evanston’s Environs

I went to Northwestern University in Evanston, Illinois to attend the excellent International Transportation Economics Association meeting (we hosted an earlier version in Minneapolis in 2009). My photos are here.

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Evanston, like Berkeley, is an historically independent city founded in the 19th century with a major university, connected by rail to the nearby city but that was fully swept into the neighboring larger city (Chicago, Oakland/San Francisco) metropolis with the growth the automobile-highway system. It is what we would today call a first ring suburb, currently housing about 75K people. The town is very pleasant and the weather, as with all my visits to Chicago, was atypically nice. It has a high income (PCI of ~$40K, especially considering that students are counting on future not present income when spending) which adds to its pleasantness, as it ensures it is well maintained, that there is new development, and that storefronts are filled. The homes are generally well-kept, and the University is very much the archetype of university architecture, with both a strong central hand ensuring buildings keep with the look and feel of the campus, and the optimal location along the Lake Michigan waterfront.

The city is more or less on a rectilinear grid plan, though there are several different plans in place which collide awkwardly in downtown. The disadvantage is the impaired navigability of such askew streets. The advantage is the heterogeneity of spaces that are created, allowing more interesting forms and spaces to be created, beyond the uniform grid. It still has the small-town feel, with many low-rise commercial structures and diagonal parking spaces in part of downtown.

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Further, (and though I did not go there since my meals were already covered) they have a Pret a Manger, which makes me jealous, as I have to rely on Jimmy Johns for sandwiches (Pret:Johns::Johns:Subway).

Like most college towns in the second decade of the twenty-first century, Evanston has decided to establish green lanes for bikes. Though I did not see many bicyclists using them, school is out of session, and Chicago has just started its bike-sharing program, putting it 3 years behind the Twin Cities.

Strangely, given the relative completeness of the Chicagoland freeway and rail systems, Evanston is not well connected to O’Hare, taxis must use surface streets for extended distances to get to the airport, while rail goes through the city of Chicago.

My favorite part of the airport trip was discovering a Cadillac dealership at Lincolnwood Town Center. Note, doing an Internet search, I find there is also a Lincoln dealership in Cadillac, Michigan. Anyway, “he meant Lexus, but he ain’t know it” (NSFW – language).

2013-07-12 at 08-05-37

Lessons from Exploring Evanston

  • College towns have a head start on economic success.
  • Exploiting naturally provided scenic beauty helps.
  • Airport access is relatively unimportant – most people are not going to the airport most of the time.
  • Locating at the edge of a metropolitan area allows the best of both worlds, access when wanted, isolation when desired.