A new quantitative evaluation methodology for transportation risk is proposed in this paper by applying the concept of ETA (Event Tree Analysis), which has been conventionally used for the risk analysis of various plant hazards. The crucial points of the proposed method lie in that it will use the ETA for describing various scenarios where the combination of various political events foreseen both domestically and internationally, would give rise to transportation risk, and that it will conduct a brain storming by participation of various specialists to reach the consensus for the evaluation results related with the possibility and effect of the scenario at hand. As a case study, a brain storming was conducted to evaluate probable transportation risk caused by interruption of sea lane for transporting energy resources in Asia-Pacific region, in order to show the detailed process of applying the proposed methodology for brain storming work by specialists, and to compare the effect of policy options available to avoid transportation risk.