Greenroads (www.greenroads.us) is a performance metric for sustainable practices associated with the design and construction of roads. It assigns points for approved sustainable choices/practices and can be used to assess roadway project sustainability measures based on total points. Such a metric can (1) provide a quantitative means of sustainability assessment, (2) allow informed sustainability decisions, (3) provide baseline sustainability standards, and (4) stimulate improvement and innovation in integrated roadway sustainability. This paper describes Greenroads version 1.0, which consists of 11 requirements and 37 voluntary practices that can be used as a project-level sustainability performance metric. Development efforts and a Washington State Department of Transportation (WSDOT) case study suggest (1) existing project data can serve as the data source for performance assessment, (2) some requirements and voluntary actions need refinement, (3) projects need to treat sustainability in a holistic manner to meet a reasonable sustainability performance standard, (4), the financial impact of Greenroads use must be studied, and (5) several pilot projects are needed. The Greenroads sustainability performance metric can be a viable means of project-level sustainability performance assessment and decision support.