subject to customs and immigration inspections. Nationals of countries other than the United States and Canada at a U.S. airport requires at least a C-1 transit visa, or ESTA for eligible travellers. Meanwhile, transiting at a Canadian airport for nationals of countries other than Canada or the United States generally requires a visa or Electronic Travel Authorization (eTA) except for individuals proceeding to or from the United States who qualify for the China Transit Program or Transit Without Visa Program. A common feature of sterile zones at airports and occasionally land and sea borders, duty-free shops sell products tax-free to customers who have cleared exit border controls prior to boarding and, in some places, to passengers arriving from overseas. Most countries impose limits on how much of each type of duty-free goods, may be purchased by each passenger. The airport with the most duty-free sales is Seoul Incheon Airport with US$1.85 billion in 2016. Dubai International Airport is second, recording transactions worth $1.82 billion in 2016. EuroAirport Basel Mulhouse Freiburg, an airport located in France 20 kilometres southeast of Mulhouse and 3.5 kilometres northwest of Basel (Switzerland), contains a binational sterile zone including a customs road allowing passengers travelling to and from Switzerland to access the airport without passing through French customs control. The airport has been jointly operated by the two countries since a 1946 treaty. Geneva Airport in Switzerland has similar facilities for French travellers. Demilitarised zones A demilitarised zone is an area in which treaties or agreements between nations, military powers or contending groups forbid military installations, activities or personnel. They often lie along de jure or de facto frontiers or boundaries between two or more military powers or alliances. Demilitarised zones should not be confused with border zones, which are areas lying along a border established unilaterally by a state for border control purposes. Many demilitarised zones are considered neutral territory because neither side is allowed to control it, even for non-combat administration. Some zones remain demilitarised after an agreement has awarded control to a state which (under the DMZ terms) had originally ceded its right to maintain military forces in the disputed territory. It is also possible for powers to agree on the demilitarisation of a zone without formally settling their respective territorial claims, enabling the dispute to be resolved by peaceful means such as diplomatic dialogue or an international court. Several demilitarised zones have