For marine traffic engineering, traffic surveys are most important and provide the fundamental materials necessary for harbour and fairway design, traffic control planning, &c. Such surveys cover numerous items, the main subjects being traffic volume, speed, distribution of ships' tracks, origin and destination and type of cargo. Since we have to deal with many vessels, handled by people with varying temperaments, knowledge and ability, observations usually show a wide scatter; the object is often to find some formula or rule to explain the phenomena, and traffic surveys are therefore apt to prove both expensive and time consuming. When, for example, Yamaguchi and others conducted a year long observation on traffic in the Akashi Channel in 1963 at least two members of the team stood watch for 24 × 365 hours in a hillside cottage making both visual and radar observations. Since then the survey has been extended to more than ten other straits well known for difficulties in manœuvring.