Winter opening of high alpine pass roads—analysis and case studies from the Swiss Alps

The pass roads across the Swiss Alps are of high importance for the transportation of persons and goods. Due to the alpine topography, most of the pass roads are permanently closed in winter, mainly because of avalanche danger. In this paper, a methodology is provided to analyse the risks for a winter opening of a pass road and to determine necessary protection measures. At first, the avalanche situation is investigated by an inventory of the existing avalanche paths. Then, a risk analysis for an initial state without any safety measures is performed. If the risks for the public and individuals are not acceptable, then protection plans taking into account preventive closures, artificial release or structural measures must be established. The acceptable risk is defined for the first time by the evaluated number of avalanches blocking an open road. The methodology was developed and adjusted with data from Flüela Pass, where over a distance of 19.3 km 47 avalanche paths endanger the road. The application of the methodology is finally demonstrated with the case studies of the Lukmanier and Gotthard Passes. For both pass roads, which were permanently closed in the past winters and which are endangered by 94, respectively, 55 avalanche paths, the SLF compiled different protection plans for a possible winter opening.