A snow shed is a
shelter over
railroad tracks, in mountainous regions where large amounts of snow fall (think the
Rockies or the
Alps). They are set up where the rail line hugs the side of a mountain, to protect the tracks from avalanches.
An example of a line with plenty of snow sheds is Amtrak's Empire Builder route, in the Glacier National Park area.
Snow sheds range in length from a dozen meters or so to an half-kilometer, depending on the terrain. They are often framed in wood, and roofed in metal or fiberglass.