The city began to face a series of problems generated by disorganized growth. Air pollution reached critical levels during the winter months and a layer of smog settled over the city. The authorities adopted legislative measures to reduce industrial pollution and placed restrictions on vehicle use. The Metro was expanded considerably, lines were extended and three new lines were built between 1997 and 2006 in the southeastern sector. A new extension to Maipú was inaugurated in 2011, at which point the metropolitan railway had a total length of 105 km. In the case of buses, the system underwent a major reform in the early 1990s. In 2007 the master plan known as Transantiago was established. It has faced a number of problems since its launch.