West Bengal has been able to attract 2% of the foreign direct investment in the last decade. Transport As of 2011, the total length of surface roads in West Bengal was over ; national highways comprise and state highways . As of 2006, the road density of the state was , higher than the national average of . As of 2011, the total railway route length was around . Kolkata is the headquarters of three zones of the Indian Railways—Eastern Railway and South Eastern Railway and the Kolkata Metro, which is the newly formed 17thzone of the Indian Railways. The Northeast Frontier Railway (NFR) serves the northern parts of the state. The Kolkata metro is the country's first underground railway. The Darjeeling Himalayan Railway, part of NFR, is a UNESCO World Heritage Site. Netaji Subhas Chandra Bose International Airport at Dum Dum, Kolkata, is the state's largest airport. Bagdogra Airport near Siliguri is a customs airport that offers international service to Bhutan and Thailand, besides regular domestic service. Kazi Nazrul Islam Airport, India's first private sector airport, serves the twin cities of Asansol-Durgapur at Andal, Paschim Bardhaman. Kolkata is a major river port in eastern India. The Kolkata Port Trust manages the Kolkata and the Haldia docks. There is passenger service to Port Blair on the Andaman and Nicobar Islands. Cargo ship service operates to ports in India and abroad, operated by the Shipping Corporation of India. Ferries are a principal mode of transport in the southern part of the state, especially in the Sundarbans area. Kolkata is the only city in India to have trams as a mode of transport; these are operated by the Calcutta Tramways Company. Several government-owned organisations operate bus services in the state, including: the Calcutta State Transport Corporation, the North Bengal State Transport Corporation, the South Bengal State Transport Corporation, the West Bengal Surface Transport Corporation and the Calcutta Tramways Company. There are also private bus companies. The railway system is a nationalised service without any private investment. Hired forms of transport include metered taxis and auto rickshaws, which often ply specific routes in cities. In most of the state, cycle rickshaws and in Kolkata, hand-pulled rickshaws and electric rickshaws are used for short-distance travel. Demographics According to the provisional results of the 2011 national census, West Bengal is the fourth-most-populous state in India with a population of 91,347,736 (7.55% of India's population). The