on-grade, the fourth sector is primarily an elevated corridor, linking Chennai Beach to Velachery and is connected with the rest of the rail network. Metro rail Chennai Metro is a rapid-transit system serving the city and was partially commenced on 29 June 2015. To improve the city's public transportation system and prepare the city for the future commuting needs, the Chennai Metro was planned and approved by the state cabinet during 2007 for which construction began on 2009. Phase I of the Chennai Metro network consists of the Blue Line and the Green Line covering a length of 45.1 kilometres (28.0 mi) consisting of 40 stations with Alandur and Chennai Central serving as interchanges. 55% of the corridors in Phase I are underground and the rest are elevated. The first stretch of Phase I, covering seven stations from Koyambedu to Alandur over a distance of , began operation on 29 June 2015. As of March 2019, the entire Phase 1 stretching from Chennai Central to Alandur on the Green line and Washermanpet to Chennai International Airport on Blue line are commercially operational, bringing the total operational network over 45 km. With this, the entirety of Phase I is operational. In December 2016, Chennai Metro Rail Limited (CMRL) announced the Phase-2 of Chennai Metro for a length of 104 km consisting of 104 stations, subject to approval from the State and Central governments. The Phase 2 was subsequently approved in late 2018, with certain provisos, and soil testing for the various stations are in full swing with construction set to begin in late 2019/ early 2020. As of April 2019 ridership has risen considerably to around 100,000 daily commuters, post the inaugural of the entire Phase I. Phase I-A, which is an extension of the Blue line from Washermanpet to Thiruvottiyur is expected to be inaugurated by June 2020. Road As of 2019, the city corporation maintains about 471 bus route roads and 33,0000 interior roads. The Chennai–Mumbai and Chennai–Kolkata prongs of the Golden Quadrilateral system of National Highways start from the city. In addition, four major National Highways (NH), namely, NH 4 to Mumbai (via Bangalore and Pune), NH 5 to Kolkata (linked via NH 6) (via Visakhapatnam and Bhubaneswar), NH 45 to Theni (via Villupuram, Tiruchirapalli and Dindigul) and NH 205 to Madanapalle (via Tirupati) originate in the city, connecting it to other Indian cities. Chennai is connected to