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The co-benefits of sustainable city projects

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C40 Cities is a network of the world's mega-cities committed to addressing climate change. In recognition of the fact that the largest cities of the world are the primary contributors to global greenhouse gas emissions, the network has conducted research into the co-benefits of sustainable city projects, examining and evaluating case studies from around the world, and across different sectors. This report summarises the findings of this research, and through the best practice guide and policy recommendations that emerge, it is hoped decision-makers will be inspired to build strong economic arguments in favour of sustainable city projects.

The five chapters that comprise the bulk of the report review how the economic benefits of green city projects have been documented in eight case studies, across five different urban sectors: public transport, with case studies on bus transit in Bogotá and Istanbul; private transportation in London and Stockholm; energy efficiency, looking at LED street lighting projects in Los Angeles and Sydney; community-scale development, specifically concerning green areas in Copenhagen; and buildings, a chapter that takes a close look at eco-roofs being built in Portland, USA.

The appendix to the report contains a best practice guide, which provides an overview of the methods involved in assessing and evaluating sustainable city projects, and how to utilise them. These include cost and benefit analysis, multi-criteria analysis, the use of proxy indicators, and others. Examples of these methods in use are provided, as well as recommendations for further reading.

Based on the case studies presented in the report, and the process of their evaluation, a number of recommendations are suggested that, if implemented, can help cities to build strong economic arguments for sustainable development:

* Increasing transparency: making data and methodology public so that others can recreate the findings helps to strengthen credibility, and will aid other cities with their own calculations.
*Undertaking comprehensive data gathering: credible calculations require credible data, both in terms of their reliability, transparency, and availability. Strategies should include: surveys to identify user behaviour and value public spaces and utilities; collecting technical data on different technologies and local meteorological and environmental conditions; the implementation of modelling to assess, for example, the efficiency of transport infrastructure; and contacting technical and social science universities to gather knowledge from the field on more complex connections and intersections.
*Making statistics more adaptable to local conditions: inputs such as income, pollution, geography, and other observable metrics should be adjusted to local contexts to increase the accuracy of the results.
*Prioritise data gathering in areas of biggest potential impact: given how costly comprehensive data gathering can be, it is a good idea to channel efforts to those areas expected to offer the most benefits.
*Build city expertise in data gathering and interpretation: it is essential to have staff with the requisite skills for gathering and interpreting data, including having contacts to universities for more detailed knowledge.