The Decision Aids for Tunnelling (DAT) are a computer based interactive tool with which tunnel construction cost, time and resource requirements can be estimated. It is possible to include uncertainties if desired and thus have results in form of distributions which are needed in modern decision making. The paper briefly reviews the basic structure of the DAT and then discusses applications such as cost, time and resource estimation for transalpine tunnels. Following this, and most important in the context of this lecture series, are applications of the DAT to compare different tunnelling technologies.