The policies of the Land Transport Authority are meant to encourage the use of public transport in Singapore. The key aims are to provide an incentive to reside away from the Central district, as well as to reduce air pollution. Singapore has a Mass Rapid Transit (MRT) and Light Rail Transit (LRT) rail system consisting of five lines. There is also a system of bus routes throughout the island, most of which have air conditioning units installed due to Singapore's tropical climate. Besides cash, a contactless smart card called the EZ-Link card can be used to pay bus and MRT fares.