Abstract
The following results were obtained from the forest road registers for privately-owned forest roads in Nagano Prefecture. Approximately 36% of the totaled routes (n = 1504) experienced no forest road facility disasters. The standard deviation of the distribution of restoration cost per affected area was 260,024,000 yen, and the distribution varied by age class. The total restoration cost analysis each year shows that 50% of the whole damage was caused by a little over 10% of the total number of damaged routes. The mean, median, and standard deviation of the restoration unit cost were 222 yen/year･m, 55 yen/year･m, and 436 yen/year･m, respectively. The restoration unit cost was <100 yen/year･m for about 59% of the total routes and <1000 yen/year･m for about 95% of the total routes, resembling a stable distribution with a heavy right hem. No clear proportional relationship was found between the number of years since opening and the restoration unit cost. The median restoration unit cost by standard was 185 yen/year･m, 71 yen/year･m, and 37 yen/year･m for Class 1, Class 2, and Class 3 forest roads, respectively. The residual standard deviation between the estimated and actual restoration unit costs calculated using the existing method is 464 yen/year･m.
