The public has to be involved in the decision making process of infrastructure projects. But the public involvement methods are more superficially used and the development decisions are often not satisfactory to the public. Therefore, a more rigorous method is needed to integrate the public or stakeholders' opinions. This paper proposes a rigor matrix to assess the quality of the decision making process and enhance the public involvement effectiveness for infrastructure projects. Focused interviews were conducted with practitioners to scrutinize the matrix's components to ensure its applicability. Rigor indices were calculated to quantify the quality of integration decisions. Finally, the rigor matrix was tested on a protested sewerage system project to explain its usefulness by comparing the actual and simulated scores. The results show that the rigor matrix and rigor indices can systematically explain and measure integration quality. This tool makes the decision making process more transparent and enhances the trust between the government and the public.