When a bridge crossing over a narrow channel is planned to construct, systematic assessment is necessary to verify how the layout of bridge piers affects to the marine traffic safety and how the safety measures are effective to improve the ship navigation safety. In the present paper, a systematic assessment procedure is proposed as to be able to solve above issues from the viewpoints of navigation difficulty, ship handling safety, aggregate evaluation and individual evaluation. And a case study was carried out to seek guidelines for bridge pier layout design and navigation safety countermeasures to be taken. From the results based on the verification employing the systematic assessment proposed, guidelines for bridge construction at sea can be found as follows; (1)Relating to the layout of piers, pier to pier distance should be designed as to be able to keep 2,000m as a rough idea. (2)Relating to the number of pier, three-piers-type makes collision risk against piers increase considerably comparing with one or two piers type. (3)Relating to traffic control to avoid encountering between ships larger than 40,000GT, this kind of traffic control based on the adjustment of estimated time of arrival has considerable effect as a safety measure.
