Coupled Transport Systems
A recent Royal Society research article considers studying different transport modes together as “coupled systems”. The road networks and public transport networks in large cities such as London and New York should be studied as a holistic system that functions together and not in isolation. As an example, the local roads may experience a peak in demand as commuters leave a station and proceed to their destination from the transport “hub”. Similarly the roads will be feeding into a train going towards the city centre in the morning rush hour. The situation is obviously more complex with metro systems, rail systems, bus networks, road transport and other modes all interacting.
Local spatial network differences can make a difference to how wider transport systems perform and interact. Studies have considered many factors in the past such as the network topology, social factors, relationships with the street network, the robustness of the network and even the evolution and the structure of the network. Coupling of networks mean that impacts are spread, sometimes on an international scale.
The research shows that, for example, increasing the speed of urban rail networks may not always beneficial. It could lead to an uneven spatial distributions of accessibility. The precise accessibility will vary according to the city based upon its morphology: London for example would need an optimal transit system speed but this would not apply in New York. The optimal speed can affect global congestion. The research suggests that it is crucial to consider the full, multi-modal, multi-layer network aspects of transport systems in order to understand the behaviour of cities. By understanding this behaviour it would be possible to avoid negative transport side-effects of urban planning decisions. A brief of the research is shown at the Royal Society web site.
This shows that multiple transport modes are being increasingly linked together but the impact varies according to the local geography. Mass transport systems can reduce congestion in city centres but actually increase it elsewhere at the transport stops or terminals. Here the road congestion becomes tied into the rail network. This model has useful implications for transport planning and needs to focus on empirical evidence of how much traffic is using each network and how they are actually linked together: if people walk from stations then there will be little impact compared with all people continuing journeys by driving cars. If modes are changed for other public transport (e.g. buses) then the impacts again will not be as great as a fewer buses accommodate many more people than many cars. Other factors such as the amount of other traffic present also affect the local congestion that can be related to the coupled systems.
This study highlights the power of geography and the advantages of considering impacts at a much more holistic level than narrower studies that focus on just single networks.
Anthropocene: the time has come?
Sometime in 2016 the case for a new geological epoch will, or will not, be made: the Anthropocene. In 2000 Paul Crutzen and Eugene Stoermer came up with the phrase to highlight the current human impact on the geological condition and processes. Human activities are impacting several areas such as:
- changes in sedimentation
- changes in sediment transport
- increases in erosion
- altering the chemical composition of the atmosphere
- alterations to the chemical composition of the oceans
- changes in chemical composition of the soils
- significant anthropogenic change in the element cycles (i.e. carbon, nitrogen, phosphorus and metal cycles)
The perturbations to processes are viewed through global warming (or Anthropogenic Climate Disruption), ocean acidification, spreading of ocean “dead zones”. There are also biospheric changes on the land and sea with habit loss, predation, species invasions as well as chemical changes.
The Quaternary working group is considering the adoption of the geological epoch the Anthropocene. It is a potential geological epoch at the same level as the Pleistocene and Holocene epochs within the Quaternary Period. It might be considered at a lower (Age) hierarchical level which would be a subdivision of the on-going Holocene epoch. Full details can be found on the Working Group on the Anthropocene web site.
There are still debates around when the epoch begun: was it the 1950’s with a “Great Acceleration” of population, industry, nuclear testing and impact on the natural world? Was it, perhaps, much earlier around the start of the industrial revolution as early as 1620? There have been debates on when the epoch begun, but the evidence is in the stratigraphy. Atmospheric carbon dioxide levels are at their highest for 800, 000 or possibly 1,000,000 years. Lewis and Maslin debated the start date in their 2015 Nature paper.
Human actions have released 555 petagrams (Pg) of carbon since 1750. 1 petagram is 10 to the power 15 grams or 1 billion metric tons. The total is therefore around 555 billion metric tons being emitted to the atmosphere. It looks likely that the impact of humans is, finally, now to be recognised with the new geological epoch: the Anthropocene.