snow shed

A snow shed is a rigid, roof-like structure built directly over a railroad track or highway to shield it from falling snow and debris during avalanche events. Unlike a full tunnel, a snow shed is typically open on the sides; it consists of a strong wooden or steel framework supporting a sloped roof that deflects material downslope rather than containing it. The shed itself becomes part of the permanent infrastructure of the line, anchored to the mountainside and designed to funnel snow and rock safely past the track below.

Snow sheds are essential in alpine and high-altitude rail corridors where deep snow accumulation and natural avalanches would otherwise force seasonal closures. The Cascade Range near Stevens Pass in Washington, the Sierra Nevada on the original Central Pacific route, and various Alpine passes in Europe all employ extensive snow shed networks. A typical shed structure is 20 to 30 feet wide, with a roof pitch steep enough (commonly 45 to 50 degrees) to prevent snow adhesion and allow material to slide clear. The shed's skeletal design reduces wind resistance compared to a full tunnel, though it still requires regular maintenance and clearing of accumulated material at its lower end.

The critical advantage of a snow shed over a snow tunnel is cost and construction speed. Tunnelling through a mountain takes months or years and demands specialized equipment; a snow shed can be erected in weeks using standard heavy timber or structural steel. However, snow sheds require ongoing labor to clear the material that accumulates at their discharge point, and in extreme conditions, the shed itself may become buried if avalanche volume exceeds the design capacity. The roof must also withstand the weight of standing snow in the lee zone, plus the impact load of falling material from above.

Early railroad snow sheds, particularly those built by the Central Pacific in the 1860s and 1870s, were constructed entirely from wood and often extended for miles across high passes. Modern variants use galvanized steel frameworks with corrugated or solid metal decking, allowing longer maintenance intervals and greater structural reliability. Some contemporary designs incorporate deflector vanes or curved roof sections to guide sliding material further away from the track or to dissipate impact energy more effectively.

Snow sheds differ from true avalanche tunnels in that they do not enclose the track completely; air flows freely around the sides and underneath. This makes them cheaper and quicker to build but requires them to be positioned only where the natural slope and terrain will ensure that deflected material does not re-enter the track zone. In areas where avalanche paths are wide or irregular, full tunnels become necessary despite their higher cost. Hybrid designs combining short tunnel sections with extended shed structures are common on modern rail lines where topology permits.