A quantitative analysis of avalanche hazard on U.S. highway 550, southwestern Colorado

Avalanches have long been a hazard on U.S. Highway 550 in the San Juan Mountains of southwestern Colorado. Historical records document numerous avalanches involving people from the 1970's to the present. Today, highway traffic is increasing due to expanding mineral exploration and developing mining, milling, and energy-related activities in and surrounding the San Juan Mountains. This paper uses avalanche event data on U.S. Highway 550, which has been documented since 1951, to calculated expected encounters between vehicles and avalanches, and to develop a hazard index for the highway. Two statistical methods are used: Poisson distribution and a method devised by Schaerer in British Columbia, Canada. Results indicate that U.S. Highway 550 can be classified as a high hazard route. These calculated expected encounters and probabilities should be considered as index values in assessing future avalanche control policies for the highway.