The Chennai Suburban Railway is a commuter rail system in the city of Chennai, Tamil Nadu, India, operated by the Southern Railways branch of Indian Railways. It is the second largest suburban rail network in terms of route length and the third largest in terms of commuters in India. Around 1,000 services are operated daily between 4:00 a.m. and midnight. It is the longest suburban circular route in India covering of 235.5 km (146.3 mi).