In a high-speed backbone network, the failure of network links may cause large data losses, so it is necessary to reserve spare network resources for faster recovery. The conventional protection methods that reserve backup paths do not consider the failure probability of each network link and allocate same amount of network resources for the backup paths regardless of the failure rate of network links. This leads to the excessive or insufficient capacity allocation. This paper proposes the routing method that guarantees the expected value of the allocated capacity based on dynamically changed link failure rate. We formulate a Mixed Integer Liner Programming (MILP) model for the proposed method. We conduct simulations to investigate the effect of the expected capacity guaranteed routing over the conventional routing method in terms of bandwidth blocking probability, transmitted capacity achieved ratio, and the ratio of total transmitted capacity to total requested capacity. The results show that our proposed method marks higher transmitted capacity achieved ratio compared to conventional routing methods. We also find the transmitted capacity achieved ratio of the proposed method maintains 90% under high failure rate.