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, litman@vtpi.org.
Summary
This paper discusses issues to consider when selecting sustainable transport indicators.
Sustainability and Sustainable Development
The concepts of sustainability and sustainable development grew from an environmental
background, but have expanded to include other issues and perspectives. The wellknown 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.
Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
Definition of Sustainable Transport
Transportation has significant sustainability impacts. Transport supports most economic
activities and social interactions, and has substantial environmental impacts. A soft
sustainability standard allows transport to increase 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 nonrenewable 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).
1
Originally developed by the Canadian Centre for Sustainable Transportation (CST, 2005).
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Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
Sustainable Transport Indicators
Indicators are 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:
1.
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.
2.
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 .
3.
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.
4.
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.).
5.
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
Pollutant
absorption
capacity
Outcome Indicator
Direction
of Change
Disaggregation
Days of poor air quality
Down
Number of at risk groups
affected
CO2 emissions
Down
n/a
2
3
Down
Total non-renewable energy
by all transport
Down
Killed and Seriously Injured
Down
Slight Casualty rates2
Down
Disaggregation
Pollutant (e.g. NOx, HC,
PM10) per capita and per
mode
By mode
Fleet average
emission rates
Down
% empty running
Down
Per capita
Mode share walk &
cycle
Up
Per km/mode
Vehicle occupancy
Up
By mode
By mode
by deprivation index and
child pedestrian deaths
Safety
Local
Quality of
Life
Air pollution
emissions
Direction of
Change
Vehicle-kms
Freight (/tonne mile)
Resource
efficiency
Intermediate
Outcomes
Vehicle-kms
Quality of transport for
disadvantaged people3
By group (disabled, older,
children, low incomes
etc.).
Up
85th percentile of
speeds
Down towards
limit for road
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...)
Up
By mode or facility
% of transport system
fully accessible
Some agreement on the right metric needs to be reached here (per capita, per trip, per-km…). I duck this debate!
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
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Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
Number of residences
exposed to aircraft noise
above 57 LAeq,T
Number of residences
exposed to noise above
55dBA
Community livability
ratings
Down
Down
By socio-economic
groups (disparity
reduction)
Up
Percentage of
residents living
within 1000m or 15minute ‘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)
Landscape
Environme
ntal
Capital
Impacts on special habitats
and environmental resources
Cumulative
impact of
policies
neutral or
beneficial
Townscape
Heritage of Historic
resources
Land paved for
transport
Per capita
Average commute
travel time
By mode
Biodiversity
Water Quality
Average freight
transport speed
Standard of
Living
Real GDP per Capita
By socio-economic group
(reducing disparity)
Up
Reliability
Up
Business/Leisure
Per capita congestion
costs
Down
By mode
Total transport
expenditures
5
Mode
Construction
Maintenance
Operation
Defining and Measuring Progress towards a Sustainable Transport System
Dr. Greg Marsden
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 carbased and
public
transport
options
Quality (availability,
speed, reliability,
safety and prestige)
of non-automobile
modes (walking,
cycling, ridesharing
and public transit).
Up
By car and public transport
Weighted journey times4 to:


Accessibilit
y


Housing
key centres of
employment;
primary, secondary &
further educational
facilities;
primary health care
provider5 & general
hospital6;
Reduced
ratio
between carbased and
public
transport
options
By car and public
transport
By income group
By age
By disability
By ethnicity
key food shops
Real lowest 10% value of
house prices within x
minutes (based on average
local journey times to
employment) of:
a) The town centre and
Disaggregat
ed by public
transport
and car
Down
b) Key centres of
employment
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
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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 indicators that 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 (www.cstctd.org); available at http://cst.uwinnipeg.ca/completed.html.
CST (2005), Defining Sustainable Transportation, Centre for Sustainable Transportation
(www.cstctd.org); at http://cst.uwinnipeg.ca/documents/Defining_Sustainable_2005.pdf.
ECMT (2004), Assessment and Decision Making for Sustainable Transport, European Conference of
Ministers of Transportation, Organization of Economic Coordination and Development (www.oecd.org).
Gudmundsson, Henrik (2001), Indicators and Performance Measures for Transportation,
Environment and Sustainability in North America, National Environmental Research Institute,
Roskilde, Denmark (www.dmu.dk/1_viden/2_Publikationer/3_arbrapporter/default.asp).
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, www.vtpi.org/wellmeas.pdf.
Litman, Todd and David Burwell (2006), “Issues in Sustainable Transportation,” International
Journal of Global Environmental Issues, Vol. 6, No. 4, pp. 331-347; at www.vtpi.org/sus_iss.pdf.
Marsden, G. Kelly, C., Nellthorp, J., Lucas, K. and Brookes, M. (2005) A Framework for the Appraisal of
Sustainability in Transport, Project Report, http://www.its.leeds.ac.uk/projects/sustainability/index.html.
WCED (1987) Our Common Future, World Commission on Environment and Development, www.un.org
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