What Does It Mean to Be Sustainable?

Most engineers today have heard of sustainability, but there are probably few who would feel comfortable defining what it means. Even well-intentioned and well-read practitioners struggle with a useful definition of sustainability. Depending on who is asked topics that fall under the umbrella of sustainability can include green materials, energy independence, pervious pavement, the heat island effect, health of local waterways, social justice, etc. The scope of topics is extremely broad and can create a lack of focus that is a barrier to making progress on technical issues and communicating an effective message about sustainability. In civil engineering, perhaps the two viewpoints on sustainability most commonly offered are a quote from the Brundtland Commission: "meeting the needs of the present without compromising the ability of future generations to meet their own needs" and the Triple Bottom Line of people, planet, and profit. These and other approaches contribute to our understanding of sustainability, sometimes from radically different points of view. In this paper the different approaches are discussed. Commonalities and differences are noted and a generalized framework of sustainability is developed. This framework can serve as a guide to analyzing some of the more popular topics in the discourse surrounding sustainability as related to civil engineering, to determine which do not fall within the scope of sustainability, which are the most important, and where we as technical practitioners should be focusing our efforts. Ultimately, the goal of this paper is to help engineers actively discuss and answer these questions for themselves.