Nebit-Dag, Ashgabat, Mary, and Chardzhou are connected by railroad to the nation's main port of Turkmenbashi on the Caspian Sea. Other lines include a railroad from Mary along the Murgab and Kushka rivers to Afghanistan and a line from Chardzhou along the Amu Dar'ya which nearly parallels Uzbekistan's border. Smaller rail spurs are located at Tashauz and Kerki. Rail lines were estimated at a total of 2,440 km (1,498 mi) in 2002. Also in 2002, there were an estimated 22,000 km (13,671 mi) of roadways, of which 18,000 km (11,185 mi) were hard-surfaced. In 2001, Turkmenistan had 76 airports, of which 13 had paved runways. In 2001, 1,407,400 passengers were carried on scheduled domestic and international airline flights.