Pan-American Highway, system of roads, c.16,000 mi (25,750 km) long, linking the nations of the Western Hemisphere. It was suggested at the Fifth International Conference of American States (1923) and supported and financed by the United States during the 1940s and 1950s. Gaps are in Panama (Darién Gap) and N Colombia, in the section called the Inter-American Highway. The route from Yaviza (Panama) to Colombia is surveyed but not constructed. The section between the United States and the Panama Canal is popular with tourists driving to Mexico. Climatic zones along the highway vary from lush jungle to cold mountain passes nearly 15,000 ft (4,572 m) high. The scenery is often spectacular, and the highway crosses many picturesque localities. The system is far from uniform; some stretches are passable only during the dry season, and in several regions driving is occasionally hazardous. In the late 1960s, much of the highway was improved.