This study investigates the factors affecting the integration of sustainability into the project management of infrastructure projects, specifically highway projects during early phases. The research was drawn upon previous studies in order to develop a sustainability framework for measuring the project success in three aspects of sustainability: People, Planet, and Prosperity (triple bottom line). Next, Critical Success Factor (CSF) framework in the construction sector was extracted through a comprehensive literature review. A qualitative cross-case analysis was conducted on three sustainability-oriented highways projects in the Netherlands. Data were collected through document review and twelve in-depth interviews with different roles of Integrated Project Management (IPM) model. The findings suggest that each IPM role is inclined towards specific sustainability dimension which affects the application of sustainability CSFs. The results reveal that among the sixteen identified CSFs promoting the integration of sustainability, following factors were acknowledged by all the IPM roles: awareness of project external factors, clearly defined scope, clearly defined goals/ambitions. Further, the paper conceptualizes a model for integrating key roles involved in the project management of infrastructure projects. The model is based on the triple bottom line of sustainability bringing all the roles involved in the project management of infrastructure projects together.