What is it?
The guiding principle of sustainability – fulfilling the needs of current generations without compromising the needs of future generations while ensuring a balance between economic growth, environmental care and social well-being – has been a central component of political and corporate objectives and declarations for several decades.
A promising pathway towards sustainability

Despite numerous earnest efforts and technological improvements, environmental sustainability has not yet been achieved, especially in the transport sector. With climate change, reaching zero emissions within less than 20 years has become the most important challenge for humanity.

Most efforts taken to reduce transport-related emissions have focused on increasing the efficiency of engines to save energy and emissions or on replacing fossil fuels with other energy sources such as hydrogen, biofuels, or renewable wind or solar energy. However, we now see that these engineered technological solutions have not helped to achieve sustainability goals – alarmingly, transport emissions have instead continued to grow.

Why have these attempts been so unsuccessful, and is there any possibility at all to achieve sustainable mobility?

How much is enough?

In general, there are several potential approaches to achieve sustainability. Developing fuel-saving engines belongs to “efficiency” strategies, meaning reducing the consumption of resources like fuel for travelling a given distance through technological improvements. Switching to alternative power sources belongs to “consistency” strategies for saving energy and resources. Although these developments are in theory very effective for reducing energy demand and emissions, reality has taught us that it seems to be impossible to realise this potential. So, what went wrong and how can it be fixed?

Cognitive science has observed that humans tend to reinvest saved costs instead of using the savings for other purposes. In parallel to the development of more and more fuel-efficient engines, the demand for larger cars has significantly increased. At the same time, the average trip distance is constantly growing, which hints to the behavioural phenomenon of constant travel time budgets, meaning that faster travel opportunities may lead to longer distances travelled rather than time saved.

This also leads to a decrease of locally accessible everyday functionalities, which is especially apparent in rural areas and residential urban areas. As a consequence, potential savings regarding resources and energy have been overcompensated, as car-dependency and vehicles sizes are increasing. Even electric mobility will not be able to turn transport towards carbon neutrality, as the demand for renewable energy cannot be met in the remaining timeframe and energy and vehicle production will remain emission intensive.


Just as much as needed

The sustainability strategies “efficiency” and “consistency” are therefore obviously not enough for reversing the unsustainable consumption of resources and the rampant emissions in the transport sector.

There is, however, a third strategy that has not yet been seriously pursued: “sufficiency”. Sufficiency basically means “as much as needed, as little as possible”.


As an example, for a short trip of about half a kilometre the choice should be to use the least-resource intensive mode available, which in this case is walking. For a longer trip or if time is an issue, cycling may be the sufficient choice. Following this principle, cars would not be legitimate options for the vast majority of trips people make.


From sufficiency to individual mobility budgets

The idea of individual mobility budgets is based on the sufficiency principle, using it as a concept for avoiding the risk of behavioural overcompensations of savings and for every person to individually achieve carbon-neutral mobility. Moreover, it provides transparency regarding the finite amount of carbon emissions our living environment can still take before becoming unhabitable. With individual mobility budgets each person is able to manage their own fair share of the overall emission budget. Just like a limited cash account, mobility budgets make us aware that we cannot spend more than is collectively sustainable.

Further Reading