Màster Oficial en Recursos Minerals i Riscos Geològics, Universitat de Barcelona - Universitat Autònoma de Barcelona, Facultat de Geologia, Curs: 2015-2016, Tutor: Joan Manuel VilaplanaThe highway C-28 is located in the Central Pyrenees and links the Aran valley with Catalonia along 20 km over the Bonaigua Pass. It constitutes a key access route for winter visitors. Most of the slopes affecting the road face to the south, with heights varying between 1600 and 2300 meters. The road runs through 58 avalanche paths of which 25 release frequently. Most of them are already capable to produce D2 or D3 avalanches, but in many places the road is carved in the hill side, what means that every single avalanche will certainly hit the road. We started from 12 years of meteorological and avalanche data collected by the local avalanche warning service of Aran Valley. Weather data were obtained from two automatic weather stations and a flowcapt, whereas avalanche activity was manually recorded in a GIS with a high level of detail. We selected 32 weather parameters including snow drift, time lagged, trend and categorical parameters and 137 avalanche days, in total. Using a classification tree method, we have developed a model to determine periods of significant avalanche activity in terms of the pre-defined avalanche day concept. The model is performed for the entire road in a combined analysis and also for three individual sections within the Pass. Results showed that time lagged conventional factors describing temperature and precipitation are more significant than the trend factors. Snow drift parameters segregated into prominent wind direction have not been found significant as solar radiation. A model for a single section with more homogeneous avalanche behavior allows us to highlight variables that were hidden in the general model applied for the overall highway.