Sudan has 4,725 kilometers of narrow-gauge, single-track railroads that serve the northern and central portions of the country. The main line runs from Wadi Halfa on the Egyptian border to Khartoum and southwest to Al Ubayyid via Sannar and Kosti, Sudan, with extensions to Nyala in Southern Darfur and Wau in Western Bahr al Ghazal, South Sudan. Other lines connect Atbarah and Sannar with Port Sudan, and Sannar with Ad Damazin. A 1,400-kilometer line serves the al Gezira cotton-growing region. A modest effort to upgrade rail transport is currently underway to reverse decades of neglect and declining efficiency. Service on some lines may be interrupted during the rainy season.