The possibility of developing high-graded forest road networks by upgrading existing ones-A widening simulation-based investigation-. J. Jpn. For. Eng. Soc. 37(1): 17 − 26, 2022. Upgrading of existing forest roads is a way of accelerating development of high-graded forest roads. However, the difficulty of upgrading in terms of physicality and economic efficiency differs by conditions of location and structure of existing forest roads. Therefore, it is unclear how amount of development of

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... aded forest roads could be achieved by upgrading. The purpose of this study is to clarify the possibility of development of highgraded forest roads by upgrading existing forest roads by use of widening simulation. The simulation was performed for forest roads located in private forest of Ina city in Nagano prefecture, and the physical availability and unit cost of widening was resulted. As a result, the ratio of the total length of routes judged to be expandable under the set conditions to the total length of the existing low-standard road network was 89.0% in the case of the expansion to 3.5 m in full width and 70.1% in the case of the expansion to 4.0 m in full width. Average widening unit cost weighted road length is 1,787yen/m in case of widening to 3.5 m full width and 5,537yen/m in case of widening to 4.0 m full width. When all existing forest roads that able to widen to 3.5 m full width on study site, it is revealed that 36% of development amount needed to achieve objective development amount are covered by widening.