We as software engineers are responsible for the long-term consequences of the systems we design - including impacts on the wider environmental and societal sustainability. However, the field lacks analytical tools for understanding these potential impacts while designing a system or for identifying opportunities for using software to bring about broader societal transformations. This article explores how the concept of leverage points can be used to make sustainability issues more tangible in system design. The example of software for transportation systems illustrates how leverage points can help software engineers map out and investigate the wider system in which the software resides, such that we can use software as an effective tool for engineering a more sustainable world. This article is part of a theme issue on Process Improvement.