Ruben Jongejan

A practical approach for the evaluation of acceptable risk in road tunnels

In many European countries it is common to adopt quantitative criteria in evaluation of acceptable risk in road tunnels. Such criteria, usually expressed by FN-criteria and IR-values, will easily lead to a regime that is difficult to adopt in practice, as the use of such criteria requires extensive analyses and documentation for all types of tunnels. In this paper, a more practical approach for the evaluation of acceptable risk in road tunnels is presented, in which quantitative risk acceptance criteria are used for some road tunnels, while qualitative criteria are used for others. This means that varying degrees of effort and documentation are necessary for the evaluation of acceptable risk in road tunnels. The approach suggested is inspired by challenges in Norway.

A risk-informed approach to coastal zone management

Economic and population growth have led to an unprecedented increase in the value at risk in coastal zones over the last century. To avoid excessive future losses, particularly in the light of projected climate change impacts, coastal zone managers have various instruments at their disposal. These primarily concern land-use planning (establishing buffer zones) and engineering solutions (beach nourishment and coastal protection). In this paper, we focus on risk mitigation through the implementation of buffer zones (setback lines). Foregoing land-use opportunities in coastal regions and protecting coasts is costly, but so is damage caused by inundation and storm erosion. Defining appropriate setback lines for land-use planning purposes is a balancing act. It is however unclear what level of protection is facilitated by current approaches for defining setback lines, and whether this is, at least from an economic perspective, sufficient. In this paper, we present an economic model to determine which setback lines would be optimal from an economic perspective. The results provide a useful reference point in the political debate about the acceptability of risk in coastal zones. The main conclusions are (i) that it is useful to define setback lines on the basis of their exceedance probabilities, (ii) that the exceedance probability of an economically efficient setback line will typically be in the order of magnitude of 1/100 per year, (iii) that it is important to distinguish between situations in which morphological conditions are stationary and non-stationary, and (iv) that long-term uncertainties (e.g. due to climate change) influence the exceedance probability of efficient setback lines but only to a limited extent.