Thoughts on the Consequences of an Increasing Personal Mobility Radius
What would an extraterrestrial observer with immense perception and processing power conclude from the movements of all humans on earth as we go about our activities? Would our busyness appear to this watcher like the busyness of bees does to us humans? Would this observer come up with theories what all our mobility is about? What would this alien scientist have to say about the evolution of our mobility? In this story I would like to a) put myself in the position of an alien studying the mobility of mankind in very abstract terms, b) try to classify the observed mobility and introduce simple metrics based on the concept of a Mobility Radius, and c) draw some conclusions for an increasing Mobility Radius on Energy Consumption.
Observed Mobility Patterns
When scientists observe bees, sometimes target animals are tagged allowing to follow their paths using a tracking system. Over time it is then possible to study and visualise the path of an individual or a collection of individuals and find some patterns in their motion like Karl von Frisch did in his pioneering work. In a similar vein, the motion of humans could be studied and described in various ways, e.g. using geo-location information gathered off their mobile phones. Potentially a mobility model could then be derived in varying levels of complexity. In the simplest case mobility could be expressed in statistical terms of a distribution of two variables in the two dimensions of the surface of our planet.
It may be possible to reduce the statistical distribution to some properties such as mean value and standard deviation. Despite all the complexity of the motion patters for humans, I would like to reduce mobility to a single figure that defines the geographical area of activity a person is likely to be found in with a degree of certainty. The simplest area that comes into my mind is a circle defined by central point and its radius, similar to mean value and standard deviation, respectively; hence the term Mobility Radius. However, I would also like to look into at least three different circumstances for which such a radius could be defined:
- Daily mobility pattern: once settled in a home most people have a daily pattern, going to school, to work, some shopping, etc. I would call that the Workday Mobility Radius or Quotidian Mobility Radius.
- Sporadic mobility outliers: beyond the daily mobility pattern are activities that go beyond that and look in statistical terms like outliers, e.g. holiday destinations, trips to visit family, etc. The mobility of this kind would be within the Holiday Mobility Radius.
- Change of mobility centre: from time to time people move, due to career choices, or migration due to political unrest. Over a life time people may have lived in one place only, or several places in one country, or all over the world. I would call that the Lifetime Mobility Radius.
More on Mobility Radius
Defining a metric for the Mobility Radius is important; for a start, we could be using the average distance travelled from a central location of the mobility case. Another approach could be to calculate some weighted Root Mean Square (RMS) of the distance to a reference point for that period as a function of time, then average over the working population. Or perhaps the integrated path length, or mileage over a period divided by that period? Even though other metrics should be possible, in the following I would like to specify the three mobility cases.
Workday Mobility Radius
It would be interesting to study in more detail the work situation of people through the centuries with respect to their commute to work, from an agrarian society and subsistence farming, over antiquity, middle ages, the industrial revolution and the associated migration to the cities up to the prediction of even more people living in urban areas. For instance, The Commuting Principle That Shaped Urban History shows how cities grew in size as the speed of locomotion increased given an acceptable commute time for most people of about 30 minutes.
In general, I am sure there is a large body of research available as a quick Google search will show, e.g. “Evolution of the average commuting time and distance in Belgium”. Most of the studies demonstrate that the distance to work has been increasing over the past decades. Infrastructure has been built to accommodate people needing to get to work; conversely, available and faster infrastructure encourages people to accept greater distance to work as long as the commute time does not increase too much: a vicious or virtuous circle that has been driving one aspect of our economies and societies: Mobility engenders more mobility.
My guestimate is that the Workday Mobility Radius is about 10km to 10 miles, if I took the work related distance from home accumulated over the work period divided by the total work time. As for its evolution, perhaps the workday mobility radius will be going down as more and more people could be working from home?
Holiday Mobility Radius
The past century has seen a steady decline in working hours and increase in paid holiday, partly due to the increase in productivity. The situation is different in most countries of the world, but in Europe most people work 35–40 hours a week, for all but 5–6 weeks of paid holiday. Whereas 100 years ago people may have had the Sunday morning off to go to church, most Western countries observe a weekend of two days, in addition to country specific national or religious holidays. It is foreseeable that the number of work hours may go down even further (as predicted by John M. Keynes). All that combined leaves a lot of scope for travel.
Again, there is lots of statistics available on the Internet on travel patterns and how they evolved over the centuries or in particular, in the past few decades. The trend has been going up, and is projected to go up even further, despite the impact of travelling on the Carbon foot print. Tourism has become global, and constitutes a large portion of revenue for many communities. How sustainable is all that? Shouldn’t we travel less rather than more, perhaps go down to the local seaside rather than travel abroad? There are many studies on that, e.g. Tourism and sustainable development.
My guestimate is that the Holiday Mobility Radius is about 100km to 100 miles, if I took the holiday related distance from home accumulated over the holiday period divided by the total holiday time. The trend is going up.
Lifetime Mobility Radius
An anthropologist could most likely give a more informed statement, but I would say that mankind has always been on the move; there were periods of migration for different reasons followed by periods of settlement, perhaps not always in phase between different regions of the world. For instance, political and economic integration in Europe made it possible for young people to study in other European countries, e.g. through the Erasmus Programme, and go and work in any country of the European Union without any limitation, the European Union’s principle of Freedom of Movement. As a consequence, a certain percentage of European students will have lived in another European country during their studies, or beyond that, they may even choose to settle in the host country.
Once more, there a lot of statistics published on the migration patterns in the world, and ways to measure migration, e.g. How far do internal migrants really move? Demonstrating a new method for the estimation of intra-zonal distance. Beyond the UK or the EU, people are studying in other countries, people are travelling farther on their holidays, people are looking for work farther away as the job market has become international. Once in a new place, temporarily or other, people are more likely to meet people of the host region or country, perhaps fall in love and settle. As a consequence, they are again more likely to travel to see family abroad; mobility begets mobility.
How do you calculate a Lifetime Mobility Radius? The world cannot be assumed to be flat; so perhaps we can calculate the RMS value of longitude and latitude difference from the birth location over a life time, then turn that into a distance through the earth radius, per person, then average over the world population? I do not know what number I should put down, but it is the evolution of that number that is important, and it is going up.
Consequences of an Increasing Mobility Radius
The need for personal mobility has always been been evolving in conjunction with the means of transport available, as these means evolved with the needs for transport: a vicious or virtuous circle, as said before: Mobility engenders more mobility.
Consequence for Energy Consumption
Given a mobility radius as a measure of distance to be travelled, what is the energy needed per person for a given transport vehicle? With m being the vehicle mass, ρ the specific density of air, Cd the drag coefficient, A the vehicle cross section, v the velocity, d the distance travelled and N the number of people the means of transport is shared between, then the energy needed to move a person over a distance d is, including the kinetic energy dissipated at the end of the journey:
The obvious interpretation of this simplistic representation is that the energy expenditure increases linearly with mass, drag coefficient, size of the vehicle as well as with distance, but follows a square law with velocity; twice the speed means four times the energy. The energy expenditure decreases as the means is shared between N people, with 1/N; this is in many ways the biggest gain in transport efficiency.
There are some cross dependencies, first between mass and number of people. The more people a vehicle is designed to transports the larger its mass is likely to be for obvious reasons. However, the kinetic energy can partly be recovered when braking if the drive train is electric, at least for wheeled vehicles. For airborne vehicles this may not really be an option and the kinetic energy will always be lost.
Another aspect is that with increasing distance the travel speed usually goes up. For instance, driving a car on a motor way is faster than in an urban environment. Train travel faster for long distance trips than trams; planes are used for very long distances and travel at higher speeds. If the speed was assumed to be conceptually proportional to the distance, v = k * d, then the energy expenditure would go up by a cubic law as a function of the distance; 2 times the distance results in 8 times the energy needed.
If an increasing mobility radius is perceived to be something positive, and if the energy expenditure has to be kept low or needs to decrease, then the means of transport has to be light, aerodynamic, slim (small cross section), shared between as many people possible, and fitted with regenerative braking, i.e. electric shuttles and buses like the ones produced by Arrival, and electric trams & trains, all perhaps autonomous in due course. If it has to be an individually owned car, then the same parameters need to be optimised; personally, I quite like designs like the Sono-Motors Sion family car. Conversely, SUVs fail on all accounts of energy efficiency.
Consequences for Society
As engineer I am not in a position really to comment on the consequences of an increase in all forms of the mobility radius, but I only would like to make one observation. Higher mobility in any shape creates links and bonds between people in different regions, countries and continents, in addition to those created through a global economy and the Internet. This, I would hope, decreases the chance of any military conflict between countries as long as governments remain democratic. It would be difficult for a politician to wind people up against other countries if nearly everybody has personal links to people in those countries, I would think. In addition, global personal links may contribute to understanding global issues that do not make halt at a national border such as climate change. Global links also foster a mindset for a global society towards a global identity. Perhaps the political motto should consequently be more like “Earth first”, or “Mankind First”.
Towards an infinite Mobility Radius
Once or if an abundant renewable energy source is available, e.g. solar power plants in the desert producing electricity galore, part of which can be used for synthetic liquid fuels, all energy worries should be gone. If then fast means of transport were available everywhere, the mobility radius could grow to an extent that everybody could move nearly anywhere, or live anywhere at very little cost. Would this create a global melting pot? The thought of an equilibrium in diffusion comes into my mind; Utopia or Dystopia; difficult to tell.
