For over fifty years, governments around the world, including in Canada, have talked about the importance of sustainability or sustainable development. The term rose to prominence through the work of the United Nations' 'Brundtland Commission', which released the report, Our Common Future, in 1987.Sustainable development, in short, means ensuring that development can meet the needs of the present without compromising the ability of future generations to meet their own needs. Sustainable development also infers that there are socioeconomic and environmental boundaries and inter-relationships that must be understood and balanced if we are to maintain the health of the plant – and our own prosperity and well-being.Sustainability has enjoyed far more talk than concrete action. Since 1990, for example, the international community has convened 12 major conferences with an aim to promote sustainability. Taken together, these high-profile events have provided a “global consensus” on the “priorities” for a new approach that reconciles the at-times competing demands of the environment, economy and society.One of the more prominent undertakings was the Rio Summit in Brazil in 1992, which led to the creation of Agenda 21. Subsequently, the Millennium Development Goals were adopted by the United Nations in 2000. These were followed by the Sustainable Development Goals (SDG's) adopted in 2015. But, yet again, we are unlikely to achieve any of the 17 SDGs by the target date of 2030. That's because our ability to achieve 'sustainability' where it counts most, at the sub-national level and in our cities, remains a significant challenge, largely because a unifying framework for making sustainable management and investment decisions is lacking. This is especially the case with infrastructure spending.Therefore, as governments contemplate massive financial stimulus in response to COVID-19, at levels far greater than the Great Recession of 2008, and now beyond the equivalent of the Depression in the 1930s, it's time to mainstream the application of sustainability cost curves, an innovative decision-making framework developed by Ontario Tech University that is being tested in the binational Great Lakes economic region in collaboration with the Council of the Great Lakes Region, as illustrated below for a series of projects in the Greater Toronto Area.Using 60 biophysical and socioeconomic indicators, built from open data sources, as a baseline for sustainability, the sustainability cost curve tool can then be used to help all levels of government, as well as private sector investors, assess and compare the sustainability impact of physical infrastructure and systems, within a city, across cities, and even at larger scales like the binational Great Lakes economic region, providing a measure of prioritization. This approach can also help to present infrastructure and investment choices to the public, as well as measure and compare the overall sustainability of a city to other cities around the world, and other regions to other regions.Sustainability Assessment of the Great Lakes – St. Lawrence RegionAs Peter Drucker once famously said, “if you can't measure it, you can't improve it.” Without consistent sustainability metrics for decision-making and investing, there is no answer to 'where are we going' and 'what impact are we having,' and there is no way to balance economic prosperity and environmental conservation.Global, national, provincial, and local sustainability goals need to be anchored together, on-the-ground. Incorporating sustainability cost curves and a 'factor of sustainability' into our infrastructure planning and decision-making, much like how an engineer defines a 'factor of safety' when designing a new building, would be an excellent start and the post-pandemic recovery provides the perfect opportunity.The alternative, spending billions of taxpayer dollars on random 'shovel-ready' projects that in the aggregate do little to build the smart, sustainable, resilient cities and infrastructure that enable us to live within society's goals and the earth's natural boundaries, is not an option. What we build today will be with us for the next 30 to 50 years. We must build sustainably!Dr. Daniel Hoornweg is the Richard Marceau research chair and an associate professor in the Ontario Tech University's faculty of energy systems and nuclear science. Mark Fisher is the President and CEO of the Council of the Great Lakes Region and an elected-school board trustee with Ottawa-Carleton District School Board. Visit city-sustainability.com for more information.