Sustainability has gained global recognition due to the detrimental effects of human activities on the environment, resulting in climate and weather extremes. In the Netherlands, the infrastructure sector is a key focus for policymakers, as it is responsible for a significant portion of the country's carbon dioxide emissions due to Factors such as non-renewable material use, machinery energy consumption, habitat destruction, and infrastructure type have contributed to its environmental impact (CO2 En Milieu, 2020). Dutch government has set ambitious goals to make the construction within the infrastructure sector more sustainable, aiming to reduce primary resource usage by 50\% by 2030 and achieve full circularity by 2030. These ambitions are outlined in regulations and policy, thus, form strategic ambitions (Ministerie van Binnenlandse Zaken en Koninkrijksrelaties, 2022). However, these strategic sustainability ambitions are often not fully realised as ambition erosion occurs (CROW, 2011). This research investigates ambition erosion and safeguarding strategic sustainability ambitions in the infrastructure sector within the construction process of the Ground, Road, Hydraulic Engineering sector, contributing to the broader sustainability transition goals and the realisation of strategic sustainability. A combination of theoretical and empirical research methods, including a literature review, semi-structured interviews with practitioners, and a case study based on an approach by Duurzaam GWW, were employed to understand the barriers and challenges associated with sustainability in the sector. The findings highlight the importance of clear and comprehensive definitions of sustainability that incorporate the three pillars of people, planet, and profit. Successful realisation of ambitions requires a clear continuation from strategic to tactical and operational levels within the exploration phase focusing on defining, establishing, specifying, and validating them. The research identifies 28 barriers categorized into capacity building, motivational, collaboration, and process-related themes. A comprehensive framework is proposed to address these barriers and reduce ambition erosion. The framework includes actions, conditions, steps, and instruments to mitigate barriers, enhance collaboration among stakeholders, and ensure a shared understanding of sustainability. The redesigned process focuses on defining, establishing, specifying, and validating strategic ambitions, with additional tools and methods incorporated for effective realisation. The proposed framework improves upon the existing approach by providing extra steps and conditions, identifying necessary actors and roles, and emphasizing collaboration and specific functions required to realize strategic sustainability ambitions. The enhancements contribute to a more effective realisation of sustainability goals at the project-specific level. This research provides valuable insights into reducing ambition erosion and safeguarding strategic sustainability ambitions in the infrastructure sector, contributing to the broader sustainability transition goals.