Traffic separation schemes have been established all over the world with the aim of reducing the danger of collision. Field observations have shown that despite the adoption by IMO and the laying down of the schemes on nautical charts a good many vessels do not comply with the steering and sailing rules applicable at traffic separation schemes. This paper attempts to review the apparent difficulties met. Some suggestions for improving of the situation are made.1. I N T R O D U C T I O N . The separation of traffic into two streams moving in opposite directions has been introduced with the aim of reducing the incidence of collisions. Such a measure results in a decrease of the rate of encounters and an almost total elimination of head-on or fine crossing meetings which are considered dangerous especially in restricted visibility. Investigations have confirmed the effectiveness of the measure in achieving the purpose provided that the steps taken are reasonable from a practical point of view.Today, traffic separation schemes are established in busy areas in many parts of the world. Despite the fact that most of these routing schemes have been adopted by IMO and details of them are depicted on nautical charts, a good number of vessels seem to have difficulties in complying with the respective rules. The purpose of this paper is, first, to show where problems affecting the safe and smooth flow of traffic arise and secondly, to indicate how these problems could be cleared away. The findings are based on long-term observations of shipping movements within and near the traffic separation schemes in the Bight of Heligoland. It is believed, however, that very similar problems exist within or near any established traffic separation scheme, so that the questions discussed here may well be of general interest.2. SPECIFICATION OF THE PROBLEM. Traffic separation schemes are intended to give order to an existing traffic situation at the price of the freedom of ship movements. Therefore, such schemes should be introduced only if they are indispensable for the maintenance or the improvement of safety. The successful working of a traffic separation scheme depends, first, on the layout of the scheme and, secondly, on the acceptance of the scheme by the users. We shall, however, not investigate the quality of any traffic separation scheme in the present paper. Nor shall we discuss whether or not in certain areas it is justified to restrict the freedom of ship movement. The concern about a possible propagation of schemes is well recognized but will remain undiscussed. We will assume at the moment that the competent authorities have made appropriate investigations before implementation of the schemes, that they have proved 398
For many practical purposes it is desirable to have a yard-stick with which safety can be measured. A criterion for the estimation of the safety of ships against collisions is outlined in this paper. The method is based on mathematical simulation and embodies all relevant factors. Numerical results are given for the English Channel and the German Bight showing the effect of parameter variations.i. I N T R O D U C T I O N . A considerable change in the size and structure of marine traffic has taken place in the last two decades. This is mainly due to the jerky rise of cargo transport across the sea and new technical developments in the recent past. The number of tankers, for example, has doubled from i960 to 1980 and their tonnage has increased sevenfold. New ship types have come into the world such as fast container ships and medium-speed vessels for the carriage of dangerous cargoes such as gas and chemical tankers. In addition, numerous structures for oil and gas production have been erected at sea which only serve to complicate marine traffic flow.Contrary to some pessimistic forecasts the transport of goods by sea will be increasing in the future and so will the number of ships at sea. The reason is that there is no other means of transport which can carry so many goods as economically as a ship.With the growth of traffic density it has been assumed that the dangers of an accident would also increase. Bearing in mind the possible consequences of a ship casualty for human life and the environment, competent authorities have, therefore, taken steps to prevent accidents. (The types of accidents considered are primarily collisions and strandings.) Measures such as separating traffic, establishing radar chains and other navigation aids, monitoring and regulating traffic, etc. were introduced. Most of these measures, however, were taken without exactly knowing what degree of safety existed before and what degree is expected after the implementation of the measure. (Clearly absolute safety is unattainable in marine traffic.) In view of the high costs associated with the measures both for the administrative authority and the user, it seems desirable to know by what amount the safety is increased.A suitable means for quantifying the safety of marine traffic seems to be the accident rate. Because of the very complex nature of marine traffic, experience and historical data alone are not sufficient to identify safety. Modern techniques for the prospective assessment of safety such as Systems Engineering, in which all relevant factors appearing in the real situation are detected and considered, 82O3 NAV 39
Depending on how the encounter rate is defined, different values can be found for the crossing angle or speed giving the smallest encounter rate. When dealing with ‘optimum crossing angles’ or ‘optimum speeds’ it is therefore proper to know which definition is taken as a basis, i.e. which expression is minimized.
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