In snowy regions, ballast may be thrown up by snow or ice stuck to the vehicle dropping off while the train is running, leading to car body damage from ballast impact. This type of snow damage also occurs in conventional railways due to the increased speed of train services; effective and economical countermeasures against such damage are urgently required.
      To obtain basic data for countermeasures through quantitative clarification of the actual conditions of the phenomenon, automatic photographing of accreted snow/ice under the vehicle floor for long periods was carried out, and weather and snowfall surveys along the railway lines during winter and investigation of the properties of accreted snow/ice under the vehicle floor were conducted. A reproduction test of ballast thrown up by the phenomenon was performed.
      The site investigation showed that accreted snow/ice under the vehicle floor builds rapidly when the daily average temperature is -4 ºC or below and the daily snowfall exceeds 3 cm (Fig. 1), the density of a mass of accreted snow/ice under the floor is 150 to 900 kg/m³ and the maximum weight of snow/ice that may drop as a mass is about 15 kg (Fig. 2). The reproduction test of the phenomenon of thrown ballast also clarified the behavior of ballast when a mass of snow hits the track surface at high speed (Fig. 3) and the relationship between the number of thrown ballast pieces and snow mass collision speed ( train speed) (Fig. 4).