Environmental Health Perspectives
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volume 122 | number 4 | April 2014
335
Research
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HTML version of th is article is available a t http://dx.doi.org/10.1289/ehp.1307250.
The Societal Costs and Benefits of Commuter Bicycling: Simulating the
Effects of Specific Policies Using System Dynamics Modeling
Alexandra Macmillan,1 Jennie Connor,2 Karen Witten,3 Robin Kearns,4 David Rees,5 and Alistair Woodward1
1School of Population Health, University of Auckland, Auckland, New Zealand, 2Department of Preventive and Social Medicine, University
of Otago, Dunedin, New Zealand; 3Social and Health Outcomes Research and Evaluation (SHORE), Massey University, Auckland, New
Zealand; 4School of Environment, University of Auckland, Auckland, New Zealand; 5Synergia Ltd, Auckland, New Zealand
Background: Shifting to active modes of transport in the trip to work can achieve substantial
co-benefits for health, social equity, and climate change mitigation. Previous integrated modeling
of transport scenarios has assumed active transport mode share and has been unable to incorporate
acknowledged system feedbacks.
oBjectives: We compared the effects of policies to increase bicycle commuting in a car-dominated
city and explored the role of participatory modeling to support transport planning in the face
of complexity.
Methods: We used system dynamics modeling (SDM) to compare realistic policies, incorporating
feedback effects, nonlinear relationships, and time delays between variables. We developed a system
dynamics model of commuter bicycling through interviews and workshops with policy, community,
and academic stakeholders. We incorporated best available evidence to simulate five policy scenarios
over the next 40 years in Auckland, New Zealand. Injury, physical activity, fuel costs, air pollution,
and carbon emissions outcomes were simulated.
results: Using the simulation model, we demonstrated the kinds of policies that would likely be
needed to change a historical pattern of decline in cycling into a pattern of growth that would meet
policy goals. Our model projections suggest that transforming urban roads over the next 40 years,
using best practice physical separation on main roads and bicycle-friendly speed reduction on local
streets, would yield benefits 10–25 times greater than costs.
conclusions: To our knowledge, this is the first integrated simulation model of future specific
bicycling policies. Our projections provide practical evidence that may be used by health and
transport policy makers to optimize the benefits of transport bicycling while minimizing negative
consequences in a cost-effective manner. The modeling process enhanced understanding by a range
of stakeholders of cycling as a complex system. Participatory SDM can be a helpful method for
integrating health and environmental outcomes in transport and urban planning.
citation: Macmillan A, Connor J, Witten K, Kearns R, Rees D, Woodward A. 2014. The
societal costs and benefits of commuter bicycling: simulating the effects of specific poli-
cies using system dynamics modeling. Environ Health Perspect 122:335–344; http://dx.doi.
org/10.1289/ehp.1307250
Introduction
Car use is the dominant mode of transport
to work in many high-income cities. In
car-oriented cities, commuting by private
motor vehicle allows access to employment
and training (crucial social determinants of
health) while enabling households to man-
age competing responsibilities. However,
car-dependent commuting has significant
negative public health effects for commuters,
the wider community, and local and global
ecosystems. A mode shift to greater use of
active transport would bring environmental,
health, social, and equity benefits (de Nazelle
et al. 2011; Hosking et al. 2011). In high-
income cities, car commutes tend to be short,
habitual, solitary trips in congested traffic.
Consequently, they make a greater contribu-
tion to road traffic injury (Bhalla et al. 2007),
air pollution and transport greenhouse gas
emissions (André and Rapone 2009), noise
(Hänninen and Knol 2011), and stress
(Jansen et al. 2003) than other kinds of light
vehicle trips. Traffic congestion at peak com-
mute times is also a significant influence on
constructing new road capacity with land
use, environmental, and social costs (Coffin
2007; Fahrig 2003). In addition, the predict-
ability of car commuting routes may make
these trips amenable to a wider range of
policy alternatives.
Previous integrated health impact assess-
ments, based on existing evidence, suggest
that a shift to human-powered transport
modes (bicycling, walking, running, wheel-
chair, skating) for short commute trips
would be good for health, aside from the
risk of road traffic injury (Hosking et al.
2011; Woodcock et al. 2009). These trips
incur negligible greenhouse gas and air
pollution costs, incorporate physical activ-
ity into people’s daily lives, and cost little
(potentially increasing equitable access to
jobs) (Hosking et al. 2011). Although trans-
port policy is identified as a determinant of
the global noncommunicable disease (NCD)
crisis, transport interventions have not been
included in the United Nations’ priority
actions for NCDs because of poor evidence
of cost-effectiveness (Beaglehole et al. 2011).
Previous comparative risk assessments have
been undertaken for transport policy, climate
change, and health (e.g., Lindsay et al. 2011;
Rojas-Rueda et al. 2011; Woodcock et al.
2009). However, these assessments have been
unable to directly compare specific policies
seeking to increase active transport, and have
not incorporated recognized system feedbacks
(Woodcock et al. 2009).
The relationships between urban
planning and health are complex, and evi-
dence for them varies widely in source and
quality. Furthermore, policies may trade gains
made against some objectives at the expense
of others. However, a set of methodological
recom mendations is emerging in the literature
that might promote effective policy decisions
in such complex systems. They include a sys-
tems approach; transdisciplinarity (integrating
knowledge across policy, community, and the
academy); community participation in deci-
sion making; and a focus on social justice and
environmental sustainability (Charron 2012).
There have been recent calls for complex sys-
tems research to tackle deep-seated problems
such as physical inactivity (Kohl et al. 2012),
obesity (Swinburn et al. 2011), and improving
the contribution of urban planning to health
(Rydin et al. 2012).
We used the principles above to develop
a commuter cycling and public health model
integrating physical, social, and environmental
well-being. We used this model to identify
Address correspondence to A. Macmillan,
Department of Preventive and Social Medicine,
University of Otago, PO Box 56, Dunedin 9056,
New Zealand. Telephone: 64 3 479 7196. E-mail:
alex.macmillan@otago.ac.nz
Supplemental Material is available online (http://
dx.doi.org/10.1289/ehp.1307250).
We thank the organizations and individuals
who participated in the interviews and workshops;
S. Turner (Beca Infrastructure Ltd) and G. Koorey
(University of Canterbury) for peer reviewing
aspects of the simulation model; and J. Woodcock
(Centre for Diet and Activity Research, Cambridge
University) for his helpful comments on an earlier
draft of the manuscript.
This research was funded by the Health Research
Council of New Zealand. A.M. also received sup-
port from the NZ Transport Agency and the NZ
Ministry of Health. D.R. is employed by Synergia
Ltd, Auckland, New Zealand.
The authors declare they have no actual or potential
competing financial interests.
Received: 19 June 2013; Accepted: 3 February
2014; Advance Publication: 4 February 2014; Final
Publication: 1 April 2014.
