A while ago I was fishing around for a suitable definition of sustainable mobility: one that would provide clarity on the trade-offs needed to evaluate the merits of one or more transport projects or services. I couldn't find one that met my needs, so I developed my own.
Most of the existing ones used circular definintions that didn't provide a basis for evaluation, or they simply assumed that certain things were inherently "sustainable". For example, one might assume that riding a bicycle is more sustainable than driving a car. A bicycle certainly produces fewer emissions (though not zero emissions, if one includes the manufacturing process), but it may not be suitable for other reasons. Consequently it might not be the most appropriate choice in some planning situations.
One definition of sustainable mobility is that used by the World Business Council for Sustainable Development as part of that organization’s Mobility Project 2030:
...mobility that meets the needs of society to move freely, gain access, communicate, trade and establish relationships without sacrificing other essential human or ecological requirements today or in the future.
I see nothing wrong with this definition, but it is not adequate as an evaluation tool for a transport planning practitioner. It needs to be unpacked in order to identify appropriate transport projects, services and strategies. This can be done by establishing a set of principles that provide a framework for policy goals that will change over time, in response to the changing status quo and political priorities. The strategies derived from these principles would not only be about the modes people are using, nor only about transportation. They would require a multi-sector, inclusive approach to planning.
I suggest the principles listed below. If you try to apply these, it will become obvious very quickly that there are no absolutes in sustainable mobility; it is about maximising sustainability performance across the set of principles, and in any given situation the trade-offs will be different.
1. Preserve the natural environment
The environment should not be degraded by transport-related activity.
2. Maintain human health and safety
Transport systems can have a direct impact on health and safety.
3. Meet the travel needs of the population
People need reliability and choice of modes in an integrated system that provides for those of all abilities and financial means.
4. Support a good economy
Transport needs to support an economy that improves the well-being of all people, with due regard to social equity.
5. Minimize transport costs for access and mobility
Reducing the cost of mobility and access will improve the ability of transport-disadvantaged people to make use of available social, cultural and economic opportunities.
6. Minimize infrastructure costs
Transport systems need to be planned in a manner that their infrastructure and services can be funded in the long term, and that best use is made of investments.
7. Maintain energy security
Transport can play a significant role in helping to decouple support of a good economy from increasing demand for fossil fuels.
8. Ensure long-term viability of the transport system
Transport infrastructure and services need to be continuously maintained; and as an integrated system, all components must work together for optimum effectiveness.
That's the short version, which doesn't fully explain the thinking behind it, so I have also prepared a complete definition of sustainable mobility. [116KB PDF] One thing that is missing from this definition is a set of indicators that could be used to carry out a rigorous evaluation based on clear measurements. That was beyond the scope of what I needed, but I think this is a useful start. I would be very interested in hearing any opinions on this. I am sure it could be improved, or perhaps someone has found another useful one. Please let me know.
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