The Danish Straits constrain access to the Baltic

Physical geography gives maritime planners relatively stable routes and constraints to examine. Traffic can avoid the English Channel by going around the rest of Britain, whereas access to the Baltic is more restricted. The Danish Straits funnel vessels into routes partly determined by their draught. The Kiel Canal provides another way through, but it is also narrow and predictable. An alternative passage therefore does not necessarily remove the strategic bottleneck.