Highways form the backbone of Pakistan's transport system; a total road length of  accounts for 92% of passengers and 96% of inland freight traffic. Road transport services are largely in the hands of the private sector. The National Highway Authority is responsible for the maintenance of national highways and motorways. The highway and motorway system depends mainly on north–south links connecting the southern ports to the populous provinces of Punjab and Khyber-Pakhtunkhwa. Although this network only accounts for 4.6% of total road length, it carries 85% of the country's traffic.