Also operated by SFMTA, the MUNI Metro is San Francisco's major light rail transit system. Trains run both underground and above ground - through streets and on street medians - with underground connections to BART along Market Street. The MUNI Metro is made up of six lines, which together carry over 160,000 riders every weekday. Given that the MUNI Metro serves many of San Francisco's neighborhoods, attractions and work zones, that's not a surprising number; the MUNI Metro is the third busiest light rail system in the U.S.