The Metropolitan Area of Mexico City is one of the largest megacities in the world. The Mexico City Subway System known as Metro, is considered an environmentally-protective transport system. The Mexico City Subway System inaugurated its first line in 1969. Presently, around 14,000 employees work in this system which covers 201.3 km allocated to eleven lines with 175 stations, through which 4.2 million commuters travel daily. It has 106 underground stations and 53 surface stations.