Canadians claim that the recently constructed Coquihalla Highway over the Rocky Mountains is one of the most spectacular and scenic superhighways in the world (Fig. 1). Unfortunately in winter snow avalanche activity is widespread and about 150 avalanche sites affect almost 17 km of the route. In one critical area a roof structure called the Great Bear Snow Shed has been constructed over the highway to protect traffic throughout the winter. This particular area of extreme avalanche hazard has a history of high avalanche frequency. Here heavy snowfall, steep terrain and adverse geological factors combine to create potentially unsafe ground above the road (Fig. 2).
The Coquihalla Highway is a four-lane dual carriage-way and the only tollway in British Columbia. It starts approximately 200 km east of Vancouver near the township of Hope on the Trans-Canada Highway and runs northeastwards for 195 km through Merritt to rejoin the Trans-Canada Highway at Kamloops. The new highway follows a series of mountain corridors through the rugged Cascade Ranges and thereby reduces the Hope-Kamloops travel distance by 80 km. The main corridors are primarily glacial in origin and contain extensive deposits of moraine and fluvioglacial drift in the valley bottoms. Along the route elevations greater than 1900 m are commonplace and relief may be as much as 1300 m. The annual snowfall in this part of the Cascade Range is usually less than 8 m, but in particularly cold years the snowpack may reach depths of more than 16 m. Extensive drifting during