The Trans-Sahara Highway is a proposed transnational highway project to pave, improve and ease border formalities on an existing trade route across the Sahara Desert. It runs between North Africa bordered by the Mediterranean Sea in the north and West Africa bordered by the Atlantic Ocean in the south, from Algiers in Algeria to Lagos in Nigeria, giving it the alternative names of the Algiers-Lagos Highway or Lagos-Algiers Highway.
The Trans-Sahara Highway is one of the oldest transnational highways in Africa and one of the most complete, having been proposed in 1962, with construction of sections in the Sahara starting in the 1970s. Its central section is still little-used though, and still requires special vehicles and precautions to be taken to survive the harsh environment and climate of the center of the desert.
The Trans-Sahara Highway has a length of about 4500 km of which about 85% has been paved. It passes through only three countries, since Algeria and Nigeria are separated by Niger alone. However, an additional 3600 km of linked highways to Tunisia, Mali and Chad are considered by planners to be integral to the Trans-Sahara Highway.
All the 1200 km of the highway lying in Nigeria is part of that country's national paved road network and includes nearly 500 km of four-lane divided sections, but highway maintenance is frequently deficient in Nigeria and at times parts of the road may be in poor condition, including having lost the pavement.
About half the highway, over 2300 km, lies in Algeria but particularly south of In Salah much of it is in poor condition, prone to flooding run-off from the Hoggar Mountains and is constantly being repaired. In 2007 the southern half of the 400 km from Tamanrasset to In Guezzam on the Niger border has been sealed. Although work continues, the rest is sand.