The Chennai Metro consists of two colour-coded lines covering a length of 54 km, making it the fourth-longest metro system in India. The system uses standard gauge and has a mix of underground and elevated stations. Construction of the Chennai Metro started in February 2009 and commercial operations started in June 2015, between Alandur and Koyambedu stations on the green line. Currently, there are two lines operational, and and three more are under construction which will cover another 116 km.