Once at a conference I was asked to briefly define sustainable transport. It wasn’t an easy task to do with a few sentences. The issue is that there isn’t a single, widely accepted definition. Also it has been changing throughout the years. This brief essay intends to collect relevant definitions adopted by major entities and by leading researchers throughout the years. It’s an attempt in describing sustainable transport in the most comprehensive way and providing a resource on how we currently see sustainable transport.

Please be aware this essay directly quotes documents and it reflects their exact wording. Sources are provided within each respective paragraph. The idea is to primarily collect and reproduce different views without analysis and stay neutral but it may not be completely free of personal opinion.

 

What is sustainable transport?

First, before we start exploring the definitions, I just want to bring you on the same page. It’s important to understand that sustainable transport isn’t an abstract concept, it’s a paradigm. We can see it being implemented and exercised everywhere around the world. Our transport system must embrace sustainable transport at a larger scale than what we can see right now.

Sustainable transport is directly linked to sustainable development which was in 1987 defined as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” by the World Commission on Environment and Development. The mentioned needs are understood as “economic development, social and human development, and environmental and ecological health” (Goldman and Gorham, 2006). Hereby, it’s important to highlight the essential needs of the world’s poor should be given priority.

Replogle, one of the first sustainable transport advocates, kickstarted the discussion around sustainable development, transport and developing countries in 1991. He highlights the need for a holistic approach covering a “diverse and balanced mix of transport modes and a sensible arrangement of land use that enables conservative use of energy and capital to fulfill mobility needs”. Further, it says that “sustainable transportation strategies are those that can meet the basic mobility needs of all and be sustained into the foreseeable future without destruction of the planetary resource base.”

Around the same time there have been many studies criticizing the automobile dependency and fossil fuel consumption, foremost led by Kenworthy and Newman. They pointed out in their 1999 publication that current “patterns of automobile dependence are not sustainable” and that we need to work towards sustainable cities.

An action plan on sustainable development was adopted in 1992 at the United Nations Conference on Environment and Development (the so-called Earth Summit). The outcome document titled Agenda 21 is the first major document adopted by global leaders with references to sustainable mobility. It describes the need for “promoting efficient and environmentally sound urban transport systems” and outlines background, objectives and potential activities for better transport.

In the same year the EU Green Paper on the Impact of Transport on the Environment introduces “sustainable mobility which should enable transport to fulfil its economic and social role while containing its harmful effects on the environment”.

In 1996, the OECD convened the Vancouver conference ‘Towards Sustainable Transportation’ and its proceedings include the following definition of environmentally sustainable transport: “Transportation that does not endanger public health or ecosystems and meets mobility needs consistent with (a) use of renewable resources at below their rates of regeneration and (b) use of non-renewable resources at below the rates of development of renewable substitutes.” The Vancouver conference proceedings concludes: “Sustainable transportation is achieved when needs for access to people, services, and goods are met without producing permanent harm to the global environment, damage to local environments, and social inequity.”

In 2001, the EU’s transport ministers adopted the following definition of sustainable transport:

• “Allows the basic access and development needs of individuals, companies and societies to be met safely and in a manner consistent with human and ecosystem health, and promises equity within and between successive generations;
• Is affordable, operates fairly and efficiently, offers choice of transport mode, and supports a competitive economy, as well as balanced regional development;
• Limits emissions and waste within the planet’s ability to absorb them, uses renewable resources at or below their rates of generation, and, uses non-renewable resources at or below the rates of development of renewable substitutes while minimizing the impact on land and the generation of noise.”

It’s described as a close adaptation of a definition by the Centre for Sustainable Transportation in Canada developed in 1997.

By 2002, the OECD has operationalized their work on environmentally sustainable transport and provided the following advanced definition in their guidelines:

• “allows generally accepted objectives for health and environmental quality to be met, for example, those concerning air pollutants and noise proposed by the World Health Organization (WHO);
• is consistent with ecosystem integrity, for example, it does not contribute to exceed of critical loads and levels as defined by WHO [other citations refer to UNECE instead] for acidification, eutrophication and ground-level ozone;
• does not result in worsening of adverse global phenomena such as climate change and stratospheric ozone depletion.”

 

UNESCAP based their working definition on the OECD and expanded it beyond environmental aspects, as reflected in their 2007 transport review:

• “is designed to contribute to reducing poverty in all its dimensions, including the elements contained in the Millennium Declaration;
• provides increasing levels of transport services that are affordable, reliable, efficient and rapid;
• minimizes resource use to sustainable levels in terms of energy, land and materials use;
• limits the public debt burden to sustainable levels (taking into account changes in public capital and operating expenditure);
• maximizes long-term economic growth that is geared to benefit all parts of the country, including the hinterlands and border regions;
• facilitates the smooth flow of goods and people across national borders, including for transit, thereby supporting regional economic integration and contributing to peace, stability and ‘good-neighbourly relations’ among countries.”

 

The meaning of sustainable transport was examined by Goldman and Gorham in 2006. They identified that definitions try either to envision sustainable transport as a policy pathway or as a policy endpoint. Their paper shows the complexity of the topic and concludes that sustainable transport represents a systems perspective.

In the business community, the relevance of sustainable transport increased in discussions on future mobility in the early 2000s. The World Business Council for Sustainable Development released in 2004 a major vision report. It includes the definition that sustainable mobility is the “ability to meet the needs of society to move freely, gain access, communicate, trade and establish relationships without sacrificing other essential human or ecological values today or in the future.”

One of the most impactful articles on this topic was written by Banister in 2008, titled “The Sustainable Mobility Paradigm”. It mentions that “the sustainable mobility approach requires actions to reduce the need to travel (less trips), to encourage modal shift, to reduce trip lengths and to encourage greater efficiency in the transport system” and “sustainable mobility has a central role to play in the future of sustainable cities, but it is only through the understanding and acceptance by the people that it will succeed”. Sustainable transport planning is outlined to focus on social dimensions, accessibility, people moving, all modes giving priority to people walking and cycling and the integration of people and traffic. Instead of looking at travel as a derived demand, the idea is to see travel as a valued activity as well.

A brief definition of sustainable mobility is given by Ieda in his 2010 book on sustainable urban mobility in Asia: “Sustainable mobility is the ability to meet society’s need to move freely, gain access, communicate, trade and establish relationships without sacrificing other essential human or ecological values, today or in the future.”

The importance of sustainable transport in global processes was confirmed again in 2015 in the 2030 Agenda for Sustainable Development where it was mainstreamed across several Sustainable Development Goals. Transport plays a major role in global policy frameworks and thus, the UN’s High-level Advisory Group on Sustainable Transport took on this topic in 2016 to outline the role of sustainable mobility for development. It defines sustainable transport as “the provision of services and infrastructure for the mobility of people and goods—advancing economic and social development to benefit today’s and future generations—in a manner that is safe, affordable, accessible, efficient, and resilient, while minimizing carbon and other emissions and environmental impacts.”  

The Global Street Design Guide by NACTO from 2016 facilitates the uptake of sustainable transport. In the glossary it defines sustainable modes as “any form of transport that is sustainable with respect to social, environmental, and climate impacts is a sustainable mode of transport. These modes do not use or rely on depleted natural resources. Instead, they rely on renewable or regenerated energy. This form of transport is socially equitable and offers increased mobility. This guide considers all active modes of transportation, collective transportation, along with vehicles using renewable energy, as sustainable modes of transportation.”

The journal article “Grand narratives for sustainable mobility” by Hoden, Banister and others in 2020 does a conceptual review of sustainable mobility. It provides the following definition: “Sustainable mobility must address the three imperatives of sustainable development: satisfying human needs, ensuring social justice, and respecting environmental limits. Subsequently, these imperatives must be translated into criteria for assessing the sustainability of the narratives. We argue that there are three such criteria: providing accessibility to basic transport (needs), ensuring equal access to transport services (justice), and ensuring that impacts of transport activities do not threaten environmental sustainability (limits).”

 

Summary

A similar exercise was done by Litman in 2013 (and last updated in 2019) in his document “Well measured – Developing Indicators for Sustainable and Livable Transport Planning”. A review drawing a brief picture about four generations of studies on sustainable mobility by Holden, Gilpin and Banister in 2019 shows: “Achieving sustainable mobility is probably the most challenging task of the plethora of tasks pertaining to the wider challenge of achieving sustainable development.”

To conclude, I threw all the definitions from this essay into a word cloud. It highlights the key words that have been used repeatedly. It shows how the paradigm of sustainable transport is centered around (environmental, economic, social) needs, development, sustainability, mobility and transport. Important elements are renewable energy, access, services, resources, health and future generations.