**12. Conclusion: A first of its kind**

The construction of the Landtunnel Utrecht at Leidsche Rijn signals the changing relation between the planning of infrastructure and the development of urban areas, as well as the coming of age of the Dutch multifunctional tunnel. With few references to fall back on, it took the involved stakeholders almost a decade (1995-2006) to agree that the environmental impact of an expanded A2 motorway required a landtunnel in order to develop Leidsche Rijn into a high-quality residential area for 30,000 homes. All stakeholders had to go through a collective learning process before they realised this fact. Environmental issues were intertwined with safety and financial issues for a long time, until a deal was reached on the project financing.

After more than a decade, it was decided in 2006 to construct the Landtunnel Utrecht as a 1650-m full-length covered tunnel, which resembles closely the initial concept that was included in the 1995 Master Plan. The path-finding process that took place between 1995 and 2006 required a unique and in-depth investigation into the interaction between (partly) covered tunnelling concepts, safety issues, noise production, air quality, financing, and urban development. Not all decisions were made according to the evidence that was produced in the process. The overall investigation can, nevertheless, be used as an evidencebased reference for the next generation of multifunctional tunnels in the Netherlands and abroad. It made clear that the motorway network in the Randstad had become an integral part of its built environment and that this fact requires new concepts and solutions.
