The Howrah–Chennai main line which runs through the state is proposed to be upgraded into a high-speed rail corridor through the Diamond Quadrilateral project of the Indian Railways. The railway network spans two zones, further subdivided into divisions – Vijayawada, Guntur and Guntakal railway divisions of South Central Railway zone, and Waltair railway division of East Coast Railway zone. There is a demand for creating a unified zone for the state based out of Visakhapatnam. There are three A1 and twenty-three A-category railway stations in the state. has been declared the cleanest railway station in the country. The railway station of Shimiliguda was the first highest broad gauge railway station in the country. As on date the Railways lines in Andhra Pradesh are under the following Railway zones/Divisions South Central Railway-Secunderabad Division South Central Railway-Hyderabad Division South Central Railway-Vijayawada Division South Central Railway-Guntakal Division South Central Railway-Guntur Division East Coast Railway- Waltair Division East Coast Railway- Khurda Road Division A new railway zone South Coast Railway Zone (SCoR) has been announced as the newest railway zone of the Indian Railways and is headquartered at Visakhapatnam, Andhra Pradesh. The formal notification for operationalization of this Zone is yet to be issued. When created it will include Waltair Division of East Coast Railway zone and Vijayawada Division, Guntakal Division & Guntur Division of South Central Railway zone. Airports Visakhapatnam Airport is the only airport in the state with operating international flights while Vijayawada Airport at Gannavaram has launched an international flight to Singapore, recently. The state has four other domestic airports, Rajahmundry Airport, Kadapa Airport, Kurnool Airport a privately owned, public use airport at Puttaparthi, and Tirupati Airport located in the city of Tirupati. There are also 16 small airstrips located in the state. Sea ports Andhra Pradesh has one of the country's largest port at Visakhapatnam in terms of cargo handling. The other famous ports are Krishnapatnam Port (Nellore), Gangavaram Port and Kakinada Port. Gangavaram Port is a deep seaport which can accommodate ocean liners up to 200,000–250,000 DWT. There are 14 notified non-major ports at Bheemunipatnam, S.Yanam, Machilipatnam, Nizampatnam, and Vadarevu. Education and research Andhra Pradesh has an overall literacy rate of 67.41% as per the 2011 Indian census. The primary and secondary school education is imparted by government, aided and private schools, managed and regulated by the School Education Department of the state. There are urban, rural and residential