Category Archives: network evolution

Accessibility and the choice of network investments in the London Underground

Recent working paper:

Levinson, D., Giacomin, D., and Badsey-Ellis, A. (2014) Accessibility and the choice of network investments in the London Underground. Presented at the World Symposium on Transport and Land Use Research, June 2014, at Delft.

Accessibility in London in 1881
Accessibility in London in 1881

 

 

  • Abstract: In 1863, the Metropolitan Railway of what came to be known as the London Underground successfully opened as the world’s first subway. Its high ridership spawned interest in additional links. Entrepreneurs secured funding and then proposed new lines to Parliament for approval, though only a portion were actually approved. While putative rail barons may have conducted some economic analysis, the final decision lay with Parliament, which did not have available modern transportation economic or geographic analysis tools. How good were the decisions that Parliament made in approving Underground Lines? This paper explores the role accessibility played on the decision to approve or reject proposed early London Tube Schemes. It finds that maximizing accessibility to population (highly correlated with revenue and ridership) largely explains Parliamentary approvals and rejections.
    Keywords: Accessibility, Network Growth, Subways, Public Transport, Travel Behavior, Networks

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.

Special Issue on the Evolution of Transportation Network Infrastructure in Networks and Spatial Economics: Volume 9, Issue 3 (2009)

A special issue of Networks and Spatial Economics on the Evolution of Transportation Network Infrastructure, for which I was the editor, is now out. Many thanks to my co-authors and the journal for making this happen. (I cannot however see the final version, as it is behind a pay-wall and my university does not yet subscribe to the journal. I have read all of the articles though, and it is well worth reading if you do have access).
Introduction to the Special Issue on the Evolution of Transportation Network Infrastructure
David Levinson
289-290
Modeling the Growth of Transportation Networks: A Comprehensive Review
Feng Xie and David Levinson
291-307
Inter-Modal Network Externalities and Transport Development: Evidence from Roads, Canals, and Ports During the English Industrial Revolution
Dan Bogart
309-338
The Efficiency of the Victorian British Railway Network: A Counterfactual Analysis
Mark Casson
339-378
Graph-Theoretical Analysis of the Swiss Road and Railway Networks Over Time
Alexander Erath, Michael Löchl and Kay W. Axhausen
379-400
Co-evolution of Density and Topology in a Simple Model of City Formation
Marc Barthélemy and Alessandro Flammini
401-425
The Topology of Transportation Networks: A Comparison Between Different Economies
Efrat Blumenfeld-Lieberthal
427-458
Jurisdictional Control and Network Growth
Feng Xie and David Levinson
459-483