Transport infrastructure networks are currently being challenged by rapidly changing contexts, such as climate change, new IT and mobility technologies, ageing infrastructure, demographic changes and growing engagement of stakeholders. These challenges call for an adaptive management approach in infrastructure planning. Apart from making the physical infrastructure more adaptive, organisational adaptive capacity is currently being discussed in both literature and practice. The literature describes learning as one of the key elements of organisational adaptive capacity. However, it remains unclear how infrastructure network agencies learn. Most of these agencies are organised in a project-oriented way. Projects can be considered as information exchange platforms of individuals that have to align their knowledge and interpretations to collectively make sense of this information to deliver a project-result. However, projects operate relatively autonomously from their parent organisation. This article aims to enhance the understanding of how projects learn from each other and how the parent organisation learns from projects and vice versa. To this end, we have conducted an in-depth case study of a typical project-oriented organisation in infrastructure planning: Rijkswaterstaat - the executive agency of the Ministry of Infrastructure and Water Management in the Netherlands. Data was collected through documents and semi-structured interviews with members of a selection of projects of Rijkswaterstaat and other members of this organisation. We used Social Network Analysis to support the analysis of the data. Subsequently, the results were confronted with literature to understand how collective learning occurs in project-oriented organisations.