WeatherWhys for February 20,2015 from accuweather.com

A snow fence is used as a shield against blowing and drifting snow. Upwind from the fence, strong winds blow falling snow or pick up snow that is already on the ground. The snow fence slows the wind, and the snow is deposited into a controlled drift. Snow fences are often set up along highways where drifting snow could become a serious travel hazard.