The organization of maritime traffic in the English Channel follows a specific pattern to ensure the safety of men and ships. Traffic is organized according to the direction of navigation of vessels. The main roads travel the four TSS (Traffic Separation Schemes) in the English Channel. These kinds of "markup" of the sea, through which ships have obligation to declare to the maritime authorities, are used to organize the important traffic. However, some areas where traffic up and down intersect are more dangerous than others. Two areas, one located in the North coast of Brittany, before entering in the Casquets TSS; and another located in the Dover Strait, just before entering in the TSS are particularly dangerous. This complex organization scheme can be explained to the narrowness of the sea and the very high density of traffic.