Transport in Croatia relies on several main modes, including transportation by road, rail, water and air. Road transportation incorporates a comprehensive network of state, county and local routes augmented by a network of highways for long-distance travelling. Water transportation can be divided into sea, based on the ports of Rijeka, Ploče, Split and Zadar, and river transportation, based on Sava, Danube and, to a lesser extent, Drava. Croatia has 68 airports, nine of which are international. The country also has several airlines, of which the most notable is Croatia Airlines. Rail transportation is fairly developed, with dual track and electrification not very common, although high-speed tilting trains are used on some routes. However, bus still tends to be more common than rail as a mode of inter-city transportation. The main form of local transportation is bus (although Zagreb and Osijek also have well-developed tram systems). Buses in major cities such as Dubrovnik, Rijeka, Split and Zadar run about once every 20 minutes, less often on Sunday. A ride is usually 10KN to 15KN, with a small discount if you buy tickets at a tisak (news-stand).