Since the beginning of 2006, bidding behavior on government construction contracts has changed from being coordination-based to being competition-based. We analyze bid data from the general public engineering works of the Shikoku Regional Development Bureau of the Ministry of Land, Infrastructure, Transport, and Tourism for the financial years from 2002 to 2011 to identify this change. The Get-Out-Dango declaration, designed to prevent bid rigging, was the main cause of the change. We support this proposition with three points of evidence: First, high-ranking public procurement involving the major players changed from coordination-based pricing to competition-based pricing. The rank order also changed, from high rank to low rank, but this order has since reversed. Second, other policy changes have had less of an impact on pricing. Finally, this behavior change had a larger effect than that of the introduction of a general competitive bidding system.

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 Mountainous areas in Japan has been exposed at the risk of rock-fall disaster. On the other hand, since the budget expensable for countermeasures against such disasters are limited, priority of the slopes at a risk of rock-fall should be discussed. In such situation, it is common to evaluate the priority of the site by cost-benefit-ratio and the benefit of the countermeasure is evaluated by the reduction of the expected economic loss. Much of researches however have pointed out the limitation of the evaluation only by the reduction of expected economic loss. This study formulates a mathematical programming problem to find an optimal strategies by minimising the weighted sum of the reductions of both expected economic loss reduction and the variance of the loss considering the budget constraints. We showed that the reduction of variance for each site is separable and the proposed model can be formulated as binary integer linear programming problem (BILP), if the occurrence probability of each slope is independent. The proposed model is first applied to the small network to see the performance, and then is applied to plan the optimal countermeasure planning of rock-fall disaster in Hida region of Gifu Prefecture. The result suggest the advantage of the proposed method.

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