Tuesday, August 30, 2016

Subways And Urban Growth: Is There A Connection?


Commuters in Tokyo, Japan
REUTERS/Kimimasa Mayama KM/CCK
Hello Everyone:

We are going to turn our attention today to the subject of transportation.  Specifically, we are going to look at a new study on the effects of the relationship between subways and urban expansion.  Our guide for this subject is Richard Florida's article CityLab article, "The Relationship Between Subways and Urban Growth."  Subway systems, across the globe have typically been thought of as way to reduce automobile traffic, ease sprawl, and provide residents with a means for affordable transportation.  The informative story focuses on the key takeaways from this study and what we can learn from it. Recently, subways have been labeled as contributors to gentrification-mechanisms for the affluent to colonize neighborhoods near stations to cut down their commutes and save time.  Mr. Florida asks, "But how do subways really affect urban development?  To what degree to promote density andante centralization?"

Construction of the Seoul metro
Seoul, South Korea

A new study, Subways and Urban Growth: Evidence from Earth (http://www.worldbank.org; date accessed Aug. 30, 2016), authored by Marco Gonzalez-Navarro of the University of Toronto and Matthew A. Turner of Brown University, sheds light on this relationship by examining "...the effect of subway location and expansion on transit ridership. population growth, and the development of urban areas."  To understand this, the authors developed a specific data set to describe all the subways systems in the world.  Their data set included information on "...underground, surface, above-ground rail transit lines, and identifies the latitude, longitude, and data of opening for every station."  They made use of nighttime satellite images (NASA satellites), calculating the light intensity gradients for each city to gauge it centralization.  Last, they culled information on populations shifts from the United Nations.  Their final analysis revealed key insights on the way subways form urban development around the world.

"Growth of subway systems"
Marco Gonzalez-Navarro and Matthew A. Turner
Most subways were built relatively recently

Americans frequently commute on transit line built around the beginning of the 20th-century.  The study found a sizable upswing in subway construction, in cities around the world, since the seventies and eighties.  Mr. Florida reports, "In total, the report identifies 7,886 operational subway stations and 10, 672 kilometers (over 6,600 miles) of subways across 138 cities as 2010.  Of these, 53 subway systems are located in Asia, 40 in Europe, 30 in North America, 14 in South America, and just one in Africa."

Bigger cities don't necessarily have larger subway systems

"Number of Stations and Subway Station (per 100,00 resident)"
Marco Gonzalez-Navarro and Matthew A. Turner

The table on the left-hand side lists the top fifteen cities around the world with at least 100 stations.  New York City heads the list with 489 stations, followed by Seoul-360, Paris-299, London-267, and Tokyo-255.  What becomes apparent is subways and subway stations follow population size.  Be that as it may, Mr. Florida points out, "But note the considerable variation in number of subway stations per 100,00 people.  New York Seoul, Paris, and London all have more subways stops than the three largest cities in the world: Tokyo, Delhi, and Mexico City."

Even though Europe cities are the smallest and growing at a slower rate, their subway systems are more expansive and the quality of service is higher than on other continents.  "All together, European subway systems serve an average of 32,000 people per station."  Specifically, more than two-thirds of large European cities have subway systems.  By comparison, North American cities have less than a third, South American cities, less than a fourth, and only 15 percent in Asia.

Conventional wisdom aside, the study concluded that subways do not necessarily jump start population growth.  Why is this, you may ask?  The reason is, even though bigger cities typically contain more extensive subway systems, the study revealed "...no correlation between the size of a system and the size of a city."  Also, while Asia is home to the majority of the world's large cities, South America is host to the largest cities, on average.  In terms of service, both of the afore contents cannot compete with the subway service in Europe and North America.  The reason for may have something to do with the fact that subways on these continents were built before automobiles went into common use and cities were smaller.  Contrast this with the fact that Asian has experienced rapid urbanization in recent years and is more dependent on automobile travel.

London Subway Map
  To measure the timing of subway construction, the study focused on the sixty-one cities that opened subway lines between 1970 and 1990.  Five years prior to the opening of the new systems, cities experienced an approximate twelve percent population growth.  However, five years after the new systems opened, population growth dropped a paltry eight percent.  The study found a similar pattern when the scope was widened to twenty years before and after new subway systems opened.  The authors observed,

...large cities build and expand subway networks but...these networks do not cause changes in subsequent population growth.  (http://www.worldbank.org; date accessed Aug. 30, 2016

This leads us to the next point.

Subway size comparison map
Subways spur decentralization

In a word, obviously.  To put more articulately, conventional wisdom says that cities with more extensive transit options tend to be denser and more concentrated around their downtown areas.  The study upends this notion.  Rather, it concluded "...that cities with larger subway systems are less centralized...the addition of one standard subway line causes a 0.5 percent decrease in centralization (measured by the concentration of satellite light) in the city center."  This result is still significantly smaller that that of road and highways, which, according to another study, are responsible for an up to nine percent decline in centralization.  Specifically the University of Toronto study found that North American cities with subway lines tend to be more spread out than most.

Be that as it may, globally, subway station are usually located close to the center, with the average density of stops and stations dwindling in context to the distance from the core.  Richard Florida writes, "On average, roughly 84 percent of subway stops are locate between 1,500 meters and 25 kilometers (about a mile to 15 miles) of the city center."

"Light and subways in 2010 for six cities"
Marco Gonzalez-Navarro and Matthew A. Turner

The image on the left-hand side is a light comparison study of subway systems, in six different sized cities, around the world: Boston, Singapore, Mexico City, Beijing, Tbilisi (Georgia), and Toulouse.  Both Tbilisi and Toulouse represent some of the smaller cities in the sample, with twenty-one and thirty-seven station respectively.  Boston and Singapore, in the second row, stand for above-average subway systems with seventy-four and seventy-eight stations each.  Finally, Mexico City and Beijing represent the largest cities in the collection with 147 and 124 stations.

In each case, the subways are typically centrally located and only a fraction of the city is located within walking distance of each station.

Subways shape greater mass transit use

Lastly, the study concluded that subways do lead to a growth in mass transit use.  Mr. Florida writes, "In a descriptive cross-sectional analysis, the authors point that cities with larger subway systems not only have more subway riders, but more bus and public transit riders in general."  However, subway expansions have a small impact on on bus ridership, despite the broader increase in public transit use.  He continues, "A 10 percent increase in subway expansion results in a 6 percent increase in subway ridership..."  Further, the authors discovered that the majority of new subway passengers are not commuters.  Yet, Mr. Florida does not elaborate on this point, although it would be mildly interesting to find out who the typical new subway rider is.  Finally, Marco Gonzalez-Navarro and Matthew A. Turner conclude that big cities cause subways not the converse. 

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