of missing links, of the five major regions—North, West, Central, East, and Southern Africa—road travel in all weather is only relatively easy between East and Southern Africa, and that relies on a single paved road through southwestern Tanzania (the Tanzam Highway). While North Africa and West Africa are linked across the Sahara, the main deficiency of the network is that there are no paved highways across Central Africa. Not only does this prevent road trade between East and West Africa, or between West and Southern Africa, but it restricts trade within Central Africa. Although there may be paved links from West, East, or Southern Africa to the fringes of Central Africa, those links do not penetrate very far into the region. The terrain, rainforest, and climate of Central Africa, particularly in the catchments of the lower and middle Congo River and the Ubangui, Sangha, and Sanaga Rivers, present formidable obstacles to highway engineers, and paved roads there have short lifespans. Further north in Cameroon and Chad, hilly terrain or plains prone to flooding have restricted the development of local paved road networks. Through this forbidding environment, three Trans-African Highways are planned to cross in the east–west direction (highways 6, 8, and 9) while one will cross north to south (highway 3). As of 2014, all have substantial missing links in Central Africa. Description of the highways in the network Nine highways have been designated, in a rough grid of six mainly east–west routes and three mainly north–south routes. A fourth north–south route is formed from the extremities of two east–west routes. East-west routes Starting with the most northerly, the east–west routes are: Trans-African Highway 1 (TAH 1), Cairo–Dakar Highway, : a mainly coastal route along the Mediterranean coast of North Africa, continuing down the Atlantic coast of North-West Africa; substantially complete, although the border between Algeria and Morocco is closed. TAH 1 joins with TAH 7 to form an additional north–south route around the western extremity of the continent. Connects with M40 of the Arab Mashreq International Road Network. Trans-African Highway 5 (TAH 5), Dakar–N'Djamena Highway, , also known as the Trans-Sahelian Highway, linking West African countries of the Sahel, about 80% complete. Trans-African Highway 6 (TAH 6), N'Djamena–Djibouti Highway, : contiguous with TAH 5, continuing through the eastern Sahelian region to Indian Ocean port of Djibouti. The approximate route of TAH 5 and TAH 6 was originally proposed in