Metro rail systems were introduced in India to address issues of unprecedented growth in personal vehicles, traffic congestion, air pollution, and accidents. India's first metro was constructed in Kolkata in 1984, while Delhi Metro began operating in 2002. There are now metros operating in many major Indian cities, with several more under construction to improve urban transport infrastructure. The document discusses the different types of metro rail systems used in India including elevated, underground, and at-grade systems as well as methods for their construction.