Masaru Matsuzawa

The influences of temperature and normal load on the shear strength of snow consisting of precipitation particles

Abstract An experiment using artificial snow was conducted to clarify the influences of temperature and normal load on temporal variations in the shear strength of snow. Artificial snow consisting of dendritic crystals was allowed to accumulate to ∼60 cm depth for the experiment. The shear strength, temperature and weight of the overlying snow were measured at three different depths in the accumulated snow. For the measurement of shear strength, the shear frame index (SFI) was found using a shear frame by placing weights with different masses on the snow contained within the frame. The measured SFI values were treated with the Mohr–Coulomb failure criterion to find the snow cohesion factor C and the internal friction factor tanϕ. The results highlighted similar trends for SFI and C values by which their rate of increase over time was greater with higher snow temperatures and normal load caused by overlying snow. This indicates that C contributes significantly to increased SFI values. tanϕ decreased over time with higher snow temperatures and increased with lower snow temperatures. In low-temperature conditions, in particular, it is likely that snow crystals are compacted but maintain their dendritic morphology.

How Drivers Perceive Visibility in Blowing Snow: Human Subject Experiments on Visibility—Viewing Videos of Blowing Snow

Road meteorological observatories measure visibility with visibility meters. However, visibility values measured by visibility meters stem from the meteorological definition, which comes from a perspective different from that of road use. Subject experiments were therefore conducted with road videos in blowing snow conditions to clarify the difference between visibility perceived by drivers and that measured with a visibility meter. The experiments revealed that visibility perceived by drivers in blowing snow was approximately 70 m lower than conventionally measured visibility. Also, a high correlation was observed between the visibility perceived by drivers and the sum total of projected area of snow particles passed through a unit area in a unit time. It was also learned that the visibility perceived by drivers during blowing snow was affected by the intensity of visibility fluctuation, the presence or absence of snowfall, road surface conditions, the surrounding environment (i.e., urban or suburban), and the time of day, and is hardly influenced at all by the direction of the snowstorm. On the basis of the above results, the need for a visibility index for road traffic in blowing snow was suggested.

Development of an Advanced Collector Snow Fence for High Embankment Road and its Effect

In cold and snowy regions, road traffic is prone to hindrance from snowstorm-induced poor visibility and snowdrifts. To mitigate these hindrances, snow fences have been installed along roads. In recent years, roads have often been constructed on high embankments, as is often seen on high-standard national highways. For roads on high embankments, collector snow fences are installed on the slopes of embankments to mitigate poor visibility from blowing snow and to secure the effective road width. In such cases, the top of the snow fence does not extend much above the road surface, which gives the fence less ability to mitigate poor visibility than for collector snow fences installed on roads without embankments. We has developed an advanced snow fence, whose performance on roads on embankments is superior to that of conventional snow collector fences. Advanced snow fences are 7 m in height. To reduce the wind pressure acting on the fence, the metal slats in the upper section are highly porous. The top third consists of mesh panel with 80 % porosity, the middle third consists of perforated slats with 30 % porosity, and the bottom third consists of non-perforated slats with 0 % porosity. The fences have proven superior to conventional snow fences in improving visibility under oblique winds.

Effects of the Provision of Wide-Area Snowstorm Information on Winter Driving

In Hokkaido, Japan, a system that provides road weather information to drivers is in operation and under further development. With regard to visibility in snowstorms, observation data collected at ground-level observation stations have been available, but not wide-area information on the distribution of visibilities. A method was developed to estimate visibility from the weather conditions, and it was applied to estimation of visibilities in a wide area. Such wide-area visibility information, together with snowfall information, was provided to road users on an experimental basis. Sixty percent of drivers who received this information changed their transportation behavior at some point, and more than 90% viewed the information as effective in increasing their sense of security. This finding confirmed that visibility information is valuable winter road information for drivers and that the visibility estimation method will be useful in providing wide-area visibility information.