The only major break in the Pan-American Highway is at Darien, between Panama and Colombia. For 160km, there is no navigable road, and trade must travel by air or sea. The lack of a link has stifled economic growth in the area, and meant that is has remained inaccessible, and a fertile ground for illegal activities (such as drug smuggling and paramilitary and terrorist groups recruitment).
It is certainly true that environmental and geographic factors mean that any link would be expensive and difficult to construct. Much of the area is undeveloped swampland and forest, the Atrato River delta in Colombia creates a marshland at least 80km wide, half of this being treacherous swampland. The Panamanian side, in contrast, is a mountainous rain forest, with altitudes reaching from 60m in the valley floors to 1,845m at Cerro Tacarcuna, the highest peak.
Efforts have been made to remove this missing link in the Pan-American highway almost since the first plans for the highway were drawn up. Serious planning began in 1971 with the help of United States funding, but this was postponed in 1974 after concerns were raised by environmentalists. A second effort began in 1992, but by 1994, this too was dropped after a United Nations agency reported that it would cause extensive environmental damage. Environmentalists argue that the lack of a road has prevented the spread of diseases such as foot and mouth (unseen in Central or North America since the 1950s), and local tribes the Embera-Wounaan and Kuna have also expressed concern that the road would help destroy their cultures. Political issues have also hindered any link, with Panamanians always remembering that they used to be part of Colombia, and while there is little risk of a Colombian army marching through Darien to forcibly reunite the countries, such concerns have now been replaced by worries about drugs and terrorists.
Consequently, nowadays the Darien Gap can only crossed by the hardiest adventurers. The first vehicular crossing of the Gap was by the Land Rovers in 1959–60, crewed by a multinational group that included Panamanians, British and Australians. Land Rover continued to show their dominance when a Range Rover on the British Trans-Americas Expedition in 1972 led by John Blashford-Snell became the first vehicle to traverse both American continents north-to-south through the Darién Gap. However, these and other crossings used boats or abandoned their vehicles and completed the crossing on foot. The first fully overland wheeled crossing (others used boats for some sections) of the Gap was by British cyclist Ian Hibell who rode from Cape Horn to Alaska between 1971 and 1973. The first all-land auto crossing had to wait until 1985–1987 by Loren Upton and Patty Mercier in a CJ-5 Jeep, taking 741 days to travel 125 miles (201 km), all on land.

