Large-sized forestry machines like harvesters and processors are commonly painted in such generally visible colors as yellow, orange or red. That use of these visible colors is effective as a passive safety measure. From a barrier-free viewpoint, it is desirable that sufficient visibility be maintained for all, including those with color blindness. Using photographs of the forestry work sites, we evaluated the CIE-L^*a^*b^* color difference between the color items under the condition of changed L and M cone sensitivity, and examined the more effective equipment color designs. In the case of such visible colors like red, orange or yellow, L^*a^*b^* color difference often declined dramatically and the color separation became lower with adjacent colors. In addition, there is no chromatic color sample that keeps fair separation with other chromatic colors. However, the installing of achromatic white, which showed good separation with other color samples as a boundary color like red-(white)-green, was able to maintain complete color separation.

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A study of change in the turbidity of water flowed from the thinned forest, using high performance forest machines in high-density forest road network was carried out. We observed that turbidity of water increased quickly and get higher just after the rainfalls. We thought the causes of these phenomena are existence of water flow routes originated from the road accompanied with the construction of road and thinning operation. The process of formation and the effects of these routes were investigated. The unstable soil displaced and deposited on the road due to the damage of road surface by repeatedly running of heavy traffics or construction of road. Such an unstable soil mass was transported by rainwater, which flowed in the forest floor from roads surface through the drainage facilities, or the collapsed roads shoulders. Some soil transported by rainwater was checked by litters in the mid way or deposited on the gently sloping forest floor which decreased the infiltration rate of forest floors and promoted the elongation of succeeding water flows downward. The environs surface water and subsurface water accumulated, and then quickly flowed into the streams. The undesirable effects are anxious concerning the water conservation function of forests, that is retardation of water inflow into the streams and averaging rate of charge adding the inflow of sedimentation into the streams. To avoid such undesirable effects, appropriate alignment of roads and drainage facilities and maintenance of its functions must be designed carefully at the time of construction of high-density road network.

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To improve traveling performance on a slope, two methods for traveling uphill using a knuckle boom crane with locus and load control function were tested using a prototype vehicle. They were 1) a method for equalizing ground contact pressure by traveling with the boom tip grounded on the downhill side of the slope, and 2) a method for combining traction with the load by the boom, which boom tip is fixed on the ground and the load is shifted toward the downslope direction. The traveling experiment confirmed that these methods were effective for improving traveling performance on a slope, because the vehicle could travel even on previously unnavigable slopes. However, it was necessary to adjust the tip load in proportion to the slope, because the traction decreased when the grounding load of the boom tip was too high. Therefore, it was confirmed that a knuckle boom crane must have a locus and a load control function, and must adjust the values using information such as inclination as a control target value, so that traveling using a knuckle boom crane may be more effective.

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