Thursday, 29 December 2016

Should historians learn system dynamics?

The magazine Mathematics Today (published by the Institute of Mathematics and its Applications) recently published an article: "Green Transport Planning Paradoxes".  The authors (Stuart Berry, Chris Parkes, University of Derby) used basic ideas of system dynamics to show that mass transport systems grow and expand until a fresh system replaces the first one.  They take as examples from UK history, the development of canals, replaced by railways, replaced by road transport, and - in some places, the introduction of mass transport rapid systems.  However, the theme of the article is that there are spin-off effects on society which are not always 100% desirable.  In particular, although mass transport rapid systems are greener than road transport, they lead to urban sprawl and increased house prices.
To illustrate their arguments, they take some simple feedback loops, such as this:
The loop works like this:
  • Rail demand growth leads to Rail network growth
  • Rail network growth leads to Travel time by rail reduction
  • Travel time by rail reduction leads to Rail demand growth
  • and
  • Rail demand growth leads to Rail network growth
and so on
The same loop applied to the boom in canals in the UK during the late 18th and early 19th centuries, until the railways provided a "better" means of transport.   So the feedback loop for canal, similar to that above, interacts with the feedback loop for rail.
But rail network growth also leads to urban sprawl and the concept of the commuter.  All over the UK there are streets of houses built during the late 19th and early 20th centuries by workers (especially office workers) who found that they could commute by rail from the nearby stations.  Now that some of those stations have closed, those houses (such as those in Okehampton, below) lack the advantages they had a century earlier.
Houses below the former station in Okehampton, near the railway, a long way from the town's main street
The same phenomenon was particularly evident in the spread of the London Underground system in the late 19th century and the first three or four decades of the 20th century. 
This is illustrated by the feedback diagram above; plus signs by an arrow mean that "up leads to up" and "down leads to down", and minus signs mean "up leads to down" and "down leads to up".  So, as rail demand increases, it leads to increased house prices, more rail development, more urban sprawl, more rail passengers, fewer road users and more rail demand. 
When I came across the article, I intended to include mention of it in this blog to ask the question - how does it apply in other nations and societies where transport systems have not followed the same successive phases of development.  In countries where there were no canals, what did the railways displace?  Can one model the growth of domestic air flights in the USA as replacements for inter-city rail travel? 
You don't need a deep knowledge of system dynamics to understand these diagrams.  But their applications are very widespread in human history.  Thanks to my flat-mate as a student, I am a co-author of a research paper in a journal of history (it gives me bragging rights in some academic circles!); he was looking at the growth of coal mining in Cumbria in the 18th century, and there were some statistical questions to be answered.  There the feedback loops were concerned with changing transport and changing technology for mining.
  • Increased demand for coal led to Expansion of the mines
  • Expansion of the mines led to Construction of wagonways to carry the coal to the port
  • Expansion of the mines led to Investment in new technology such as steam pumps
  • Investment in new technology led to (eventually) Reduced prices for coal
  • Construction of wagonways to carry the coal to the port led to Reduced prices for coal
  • and
  • Reduced prices for coal led to Increased demand for coal
More recently, I picked up a book in Exeter Library which - at first sight - seemed to have been shelved in the wrong place.  It was about the history of Roman roads in Britain, and had been shelved with books on warfare.  It transpired that the author's thesis was that the road system in Britain was not created by the Romans, but the Roman occupation was one element in its development.  Roads pre-dated the arrival of the Romans in 43AD, and the system developed to meet the needs of successive rulers, through medieval times to modern days.  The author catalogued numerous battles fought on British soil (hence the library's shelving) and their proximity to the major roads of the country.  With system dynamics in my head, I thought that the book had missed a trick or two by ignoring feedback loops.  Two struck me:
  • Increased unrest in the land leads to Increased military strength by the ruler
  • Increased military strength by the ruler leads to Increase in the road system
  • Increase in the road system leads to More communication of grievances among the populace
  • More communication of grievances among the populace leads to Increased unrest in the land
  • and so on

and
  • More subdivision of the land into power blocs leads to More strife at the boundaries
  • More strife at the boundaries leads to Reduction in transport between the blocs
  • Reduction in transport between the blocs leads to Deterioration of roads between blocs
  • Deterioration of roads between blocs leads to More subdivision of the land into power blocs
  • and so on 

So, maybe historians should learn system dynamics.

References:  Green Transport Planning Paradoxes by Stuart Berry and Chris Parkes: Mathematics Today, volume 52, no 4, August 2016, pp193-197
The Secret History of the Roman Roads of Britain by M C Bishop (Pen and Sword, 2014, ISBN 978 1 84884 615 9) 
The Land Tax Returns as a Source for Studying the English Economy in the Eighteenth Century by J V Beckett and D K Smith Bulletin of the Institute for Historical Research 54(129):54 - 61

2 comments:

  1. The article is the best way to see what we deal with because of urban growth pattern. This reinforces the biblical view of how joining field to field or house to house is never the best way to live.

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    1. Jeremiah Fanning is quoting from Isaiah chapter 5 verse 8, which reads "Woe to you who add house to house and join field to field till no space is left and you live alone in the land." On this passage, the commentator Matthew Henry wrote: "Here is a woe to those who set their hearts on the wealth of the world. Not that it is sinful for those who have a house and a field to purchase another; but the fault is, that they never know when they have enough. Covetousness is idolatry; and while many envy the prosperous, wretched man, the Lord denounces awful woes upon him." There is clearly a feedback loop hinted at in the prophet's words, but it is NOT the same as the one I am referring to in the blog. It is the feedback loop of personal covetousness, which is different from the societal behaviour in response to changed infrastructure of which I was writing. The verse from Isaiah is cross-referenced to several others which condemn unjust means for gaining land, and comes in that context in chapter 5

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