Suburban railway and BEST bus services together accounted for about 88% of the passenger traffic in 2008.[54] Auto rickshaws are allowed to operate only in the suburban areas of Mumbai, while taxis are allowed to operate throughout Mumbai, but generally operate in South Mumbai.[55] Taxis and rickshaws in Mumbai are required by law to run on compressed natural gas (CNG),[56] and are a convenient, economical, and easily available means of transport.[55]