must be used when snow is deeply drifted and tightly packed. However, they pile snow close to the track,
making it difficult to plow later snowfalls. They also require considerable maintenance.
4.16.
SNOWSLIDES AND SNOWDRIFTS
Snowslides are much worse than plain snowdrifts because they may be filled with trees and rocks. The
amount of snow in a slide usually rules out using any plows except the rotary type. However, if a snowslide is
suspected of containing rocks and trees, the rotary plow cannot be used because its blades may be damaged.
Handtools, dynamite, or bulldozers or other excavators must be used.
4.17. SNOW FENCES AND SHEDS
Snow fences and snow sheds are often used to protect sections of a railroad that are continually subjected
to drifts and slides because of peculiar terrain features.
a. Snow fences are used to prevent drifts from piling up on the track. One type is made of light wood
slats wired together and looks something like a long venetian blind set on edge. It comes in sections of various
lengths and can be rolled up for easy carrying or storage. In use, it is set up with the slats sticking up from the
ground, parallel to and some distance away from the track on the side from which the wind is expected. The
wind velocity is reduced as it passes through the slats. As a result of the decreased velocity, the snow drops and
piles up forming a drift around the fence before it can reach and obstruct the track. Several other types of either
metal or wood for temporary or permanent construction as well as hedges and stone fences may also be used.
b. Snow sheds protect against slides in side hill cuts and against drifts and slides in through cuts. They
provide direct shelter for the track so that a tunnel under the snow is open for traffic. They are permanent and
most often constructed of timber.
4.18.
PROBLEMS WITH SWITCHES AND MOVABLE POINT FROGS
The points of switches and movable point frogs and the car retarders in automatic hump yards may be
frozen or blocked in place by ice or snow. Restriction of their movement blocks sidings and terminals, often
tying up whole divisions or even systems. Several ways of meeting the problem are discussed in the
subparagraphs that follow. However, during severe snowfalls, these procedures may
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