Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
Defining and Measuring Progress Towards Sustainable Transport
Discussion Paper
12 September 2007
Sustainable Transportation Indicators (STI)
Transportation Research Board Subcommittee (ADD40 [1])
Send comments to:
STI Subcommittee Chair Todd Litman, .
Summary
This paper discusses issues to consider when selecting sustainable transport indicators.
Sustainability and Sustainable Development
The concepts ofsustainability and sustainable development grew from an environmental background,but have expanded to include other issues and perspectives. The well-known Bruntland report defines it as “Economic and social development that meets the needs of the current generation without undermining the ability of future generations to meet their own needs" (WCED, 1987). This definition brought together what is commonly referred to as the three pillars of sustainable development; economic, social and ecological (or environmental). Some recent definitions incorporate other factors such as governance and financial sustainability.
Sustainability maintains a distinction between growth (increased quantity) and development (increased quality). It focuses on social welfare outcomes, such as human health and education attainment, rather than simply measuring material wealth, and questions common economic indicators such as Gross Domestic Product (GDP) that measure only the quantity but not the quality of market activities.
The notion of sustainability is not specific to any geographic area. Sustainable development must ultimately be global, with individual jurisdictions contributing to specific goals, such as sustainable economic development, social equity and environmental protection. However, there are yet no universally accepted sustainability goals or frameworks for distributing the responsibilities for achieving those goals among different jurisdictions and sectors. An example of international goal-setting is the Kyoto Protocol, which sets climate change emission reduction targets, and as of June 2007 had 174 signatory countries, although some of the largest emitters have yet to sign.
Sustainability can be evaluated based on a “soft,” flexible standard, which allows natural capital (that is, natural environmental resources and ecological systems) to be replaced by human capital, or a “hard” standard, which rejects such substitutions. For example, soft sustainability allows depletion of wild fish stocks if aquaculture can result in equal or greater fish food production. Hard sustainability requires that wild fish stocks be preserved.Hard sustainability places more emphasis on environmental preservation, shifting the burden of proof to favor ecological preservation over industrial growth.
Definition of Sustainable Transport
Transportation hassignificant sustainability impacts. Transport supports most economic activities and social interactions,and has substantial environmental impacts. A soft sustainability standard allows transport toincrease environmental impacts if required for economic development, or if negative impacts can be offset by other sectors, such as reductions in pollution emissions by heavy industries.A hard sustainability standard tends to place more emphasis on reductions of impacts within the transportation sector, and therefore places more emphasis on reducing motor vehicle ownership and use.
Several definitions of sustainable transportation have been proposed (Litman, 2007). Of them, we recommend the definition selected by the European Council of Ministers of Transport,[1] because it has a broad scope, recognizing that sustainability includes economic factors, such as affordability and efficiency, and social factors, such as equity and human health, in addition to environmental sustainability.
A sustainable transport system (ECMT, 2004):
- Allows the basic access and development needs of individuals, companies and society to be met safely and in a manner consistent with human and ecosystem health, and promotes equity within and between successive generations.
- Is affordable, operates fairly and efficiently, offers a 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 the use of land and the generation of noise.” (ECMT, 2004).
Key Definitions (based on Gudmundsson, 2001)
Baseline (or benchmark) – existing, projected or reference conditions if change is not implemented.Goal – what you ultimately want to achieve.
Objective – a way to achieve a goal.
Target – A specified, realistic, measurable objective.
Indicator – a variable selected and defined to measure progress toward an objective.
Indicator data – values used in indicators.
Indicator framework – conceptual structure linking indicators to a theory, purpose or planning process.
Indicator set – a group of indicators selected to measure comprehensive progress toward goals.
Index – a group of indicators aggregated into a single value.
Indicator system – a process for defining indicators, collecting and analyzing data and applying results.
Indicator type – nature of data used by indicator (qualitative or quantitative, absolute or relative).
Sustainable Transport Indicators
Indicatorsare variables selected and defined to measure progress toward an objective. Which indicators are selected, and how they are defined and measured, can significantly affect planning decisions. A particular activity or option may appear desirable when evaluated using one set of indicators and less desirable when evaluated using another.
Sustainable transport indicators measure progress toward sustainable transportation. Many possible sustainable transport indicators (more than one hundred) have been proposed. It is important to select and define a set of indicators that provide effective guidance for transport policy and planning analysis.
The following are key principles that should be considered when selecting sustainable transportation indicators:
- Headline indicators should be outcome oriented
Sustainability reflects issues such as the ability of the atmosphere to absorb pollutants. A suitable outcome indicator would therefore be “the number of days of poor air quality” rather than “the emissions of toxic pollutants”. For safety absolute numbers of injury accidents would be a key metric.
- A direction of change should be specified
Sustainability is often measured in relative rather than absolute units. In many cases it is possible to identify the desired direction of change as an indicator of sustainability even if no specific target is defined.For example, it may difficult to define a specific sustainable level of per capita energy consumption, pollution emissions or transportation affordability, but it may be reasonable to specify that energy conservation, emission reductions and improved transportation affordability reflect progress toward sustainability .
- Policy targets should be included where relevant
In some instances (e.g. CO2 emissions, renewable energy usage), policy targets are established through a political process. Whilst these targets may be somewhat arbitrary, they can be helpful in determining whether progress is being made within a sector and provide more information than merely a direction of change that would otherwise be adopted.Such targets may be modified over time based on greater scientific understanding.
- Indicators should be disaggregated appropriately
Health-related indicators often seek to reduce the impacts on those most at risk (e.g. road safety indicators can be focused both on the population at large at children from more disadvantaged backgrounds, air quality standards are set at levels to protect those with respiratory problems). Sustainability suggests social progress and therefore the need to consider what progress means to different social groups (cost of travel relative to incomes etc.).
- Supporting intermediate outcomes should be specified
The set of key outcome indicators should be consistent with the national strategy. However, it is essential to have an understanding of what changes in the transport system will drive changes to the key outcomes. Here it may be important to consider how different indicators vary by mode (e.g. energy use per person kilometer versus energy use per tonne kilometer).
Prioritizing Sustainable Transport Indicators
Table 1 lists various sustainable transportation indicators, based on previous analysis by the Centre for Sustainable Transportation (2003), Marsden, et al. (2005), and Litman (2007). It indicates the desired direction of change, and whether an indicator is an “intermediate” stop or an ultimate “outcome,” and possible disaggregations.
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Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
Table 1: Draft list of TRB Sustainability Indicators(CST, 2003; Marsden, et al., 2005; Litman, 2007)
Area of Progress / Outcome Indicator / Direction of Change / Disaggregation / Intermediate Outcomes / Direction of Change / DisaggregationPollutant absorption capacity / Days of poor air quality / Down / Number of at risk groups affected / Air pollution emissions / Down / Pollutant (e.g. NOx, HC, PM10) per capita and per mode
CO2 emissions / Down / n/a / Vehicle-kms / By mode
Fleet average emission rates / Down / By mode
Resource efficiency / Total non-renewable energy by all transport / Down / Freight (/tonne mile) / % empty running / Down
Per capita / Mode share walk & cycle / Up
Per km/mode / Vehicle occupancy / Up / By mode
Safety / Killed and Seriously Injured / Down / by deprivation index and child pedestrian deaths
Slight Casualty rates[2] / Down / Vehicle-kms
85th percentile of speeds / Down towards limit for road
Local Quality of Life / Quality of transport for disadvantaged people[3] / Up / By group (disabled, older, children, low incomes etc.). / Overall transport system satisfaction rating / Up / By group (disabled, older, children, low income...)
Usage of transport system / Up / By group (disabled, older, children, low income...)
% of transport system fully accessible / Up / By mode or facility
Number of residences exposed to aircraft noise above 57 LAeq,T / Down
Number of residences exposed to noise above 55dBA / Down
Community livability ratings / Up / By socio-economic groups (disparity reduction) / Percentage of residents living within 1000m or 15-minute ‘safe walk’ to key destinations (e.g. health, educational, food shops etc.) / Up / by groups (e.g. primary school by % of children under 11 years)
Environmental
Capital / Impacts on special habitats and environmental resources / Cumulative impact of policies neutral or beneficial / Landscape
Townscape
Heritage of Historic resources
Biodiversity
Water Quality / Land paved for transport / Per capita
Standard of Living / Real GDP per Capita / Up / By socio-economic group (reducing disparity) / Average commute travel time / By mode
Average freight transport speed
Reliability / Up / Business/Leisure
Per capita congestion costs / Down / By mode
Total transport expenditures / Mode
Construction
Maintenance
Operation
Poverty / Affordability (portion of household budgets devoted to transport). / Reduction in burden to poorest / By socio-economic group / Average real cost of journey to key destinations / Reduced ratio between car-based and public transport options / By car and public transport
Accessibility / Weighted journey times[4] to:
- key centres of employment;
- primary, secondary & further educational facilities;
- primary health care provider[5] & general hospital[6];
- key food shops
By income group
By age
By disability
By ethnicity / Quality (availability, speed, reliability, safety and prestige) of non-automobile modes (walking, cycling, ridesharing and public transit). / Up
Housing / Real lowest 10% value of house prices within x minutes(based on average local journey times to employment) of:
a)The town centre and
b)Key centres of employment / Disaggregated by public transport and car / Down
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Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
Where next?
Our ultimate goal is to help create an analysis framework and a functional set of sustainable transportation indicatorsthat can be endorsed by the Transportation Research Board and other professional organizations.It may require further development of the indicator set listed in Table 1, including:
- Additional definitions to reflect additional impacts of concern.
- Clearer definitions to minimize confusion.
- Prioritization, to indicate which indicators are most important.
- Consideration of data availability and quality, so recommended indicators are feasible and accurate.
- Discussion of ways to create indices aggregated a group of indicators into a single value.
Our next steps will be to evaluate the indicators in Table 1, identify possible omissions and points of confusion, and discuss the basis on which they can be prioritized. After we have made progress within our Subcommittee, we can share the results with groups such as the Energy and Social Factors committees. Critical to this process is managing the process so the results are technically accurate and useful for decision-making (see Gudmundsson, 2003 for the pitfalls of not doing this).
References
CST (2003), Sustainable Transportation Performance Indicators, Centre for Sustainable Transportation ( available at
CST (2005), Defining Sustainable Transportation, Centre for Sustainable Transportation ( at
ECMT (2004), Assessment and Decision Making for Sustainable Transport, European Conference of Ministers of Transportation, Organization of Economic Coordination and Development (
Gudmundsson, Henrik (2001),Indicators and Performance Measures for Transportation, Environment and Sustainability in North America, National Environmental Research Institute, Roskilde, Denmark (
Gudmundsson, H. (2003) Making concepts matter: sustainable mobility and indicator systems in transport policy, International Social Sciences Journal 176 p199-217
Litman, T. (2007) Well Measured Developing Indicators for Comprehensive and Sustainable Transport Planning,
Litman, Todd and David Burwell (2006),“Issues in Sustainable Transportation,”International Journal of Global Environmental Issues, Vol. 6, No. 4, pp. 331-347; at
Marsden, G. Kelly, C., Nellthorp, J., Lucas, K. and Brookes, M. (2005) A Framework for the Appraisal of Sustainability in Transport, Project Report,
WCED (1987) Our Common Future, World Commission on Environment and Development,
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[1] Originally developed by the Canadian Centre for Sustainable Transportation (CST, 2005).
[2]Some agreement on the right metric needs to be reached here (per capita, per trip, per-km…). I duck this debate!
[3]This needs to be more clearly defined. I think if it is in the options available for people to use then user satisfaction, patronage become meaningful intermediate outcomes
[4] It may be advisable to also include cost of journey to these destinations with some indication of costs over e.g. $2 being non-affordable for low-income households and highlighting disparities in cost between car and public transport
[5]Doctor’s surgery, health centre, NHS walk-in centre
[6]Hospital offering A&E and other key services