Urban areas are becoming increasingly more complex to plan as they face rising demands for sustainable development, resilience to climate change, and efficient use of space. At the same time, infrastructure projects are growing in size and complexity, often affecting multiple sectors at once. Among the most critical of these are the transport and water sectors, which historically have been addressed through separate planning processes. However, their growing independence, particularly in dense and hydrologically sensitive cities, highlights the need for more integrated approaches.This thesis investigates how transport and water infrastructure can be planned in a more coordinated way to support sustainable urban development. A comparative study is conducted of two major infrastructure projects in Europe: the E4 Förbifart Stockholm highway project in Sweden and the Vienna U2xU5 metro expansion in Austria. Both projects involve extensive underground construction in urban environments and interact directly with groundwater systems, making them highly relevant for analyzing cross-sector collaboration. The study uses a qualitative research method, including analysis of planning documents, policy frameworks, and academic literature. It explores how integration between the two sectors is handled during the planning and implementation phases, what governance structures and regulations influence this process, and what lessons can be learned from each city.The conclusion suggests that, while both Stockholm and Vienna recognize the value of integrating the transport and water sectors, they implement it differently based on institutional structures, planning cultures, and urban policy goals. Stockholm demonstrates a strong environmental regulatory framework, but with limited coordination between the two sectors. Vienna, on the other hand, applies a more centralized and climate-focused strategy, allowing for a more structured integration.Finally, the thesis argues that an integrated planning between transport and water infrastructure is essential, not only to reduce environmental risks, but also to enhance urban resilience and functionality. By highlighting practical examples and governance challenges, the study contributes to the broader discussion on cross-sector collaboration as a necessary component of sustainable urban development.