Southwest is headquartered in Downtown at GreenStreet. Transportation The Metropolitan Transit Authority of Harris County (METRO) operates Houston's public transportation systems. Downtown lies at the convergence of the three lines of Houston's light rail system, known as METRORail. The Red Line, which runs along Main Street, contains the following stations (from south to north): Downtown Transit Center, Bell, Main Street Square, Preston, and . The Southeast/Purple Line and East End/Green Lines stop at the Central, Convention District, and Theater District stations. METRO operates many bus lines through Downtown. Greenlink, a free-to-ride circulator shuttle, follows a circular route around the district. Greenlink is the successor to a trolley-style free-to-ride bus service which carried over 10,000 riders each day on five different routes prior to its disbandment in 2005. Taxicabs can be hailed from the street, at one of 21 taxi stands, or at various hotels. Taxi trips within Downtown have a flat rate of US$6, mandated by the city. Uber operates within the city and surrounding areas. Education Colleges and universities The University of Houston–Downtown (UHD) is a four-year state university, located at the northern-end of Downtown. Founded in 1974, it is one of four separate and distinct institutions in the University of Houston System. UHD has an enrollment of 14,255 students—making it the 15th largest public university in Texas and the second-largest university in the Houston area. The South Texas College of Law is a private law school located within Downtown and is one of three law schools in Houston. Downtown is within the Houston Community College System, and it is in close proximity to the Central Campus in Midtown. Primary and secondary education Public schools The grade-school children of Downtown are served by the Houston Independent School District (HISD). One public K-8 school, an HISD-affiliated charter school called Young Scholars Academy for Excellence (Y.S.A.F.E.), is in Downtown. It was established on May 15, 1996 by Kenneth and Anella Coleman. HISD's High School for the Performing and Visual Arts (HSPVA), a public magnet high school, broke ground on a new downtown campus in 2014, and classes began there in 2019, replacing HSPVA's previous Montrose-area campus. Three public district elementary schools have zoning boundaries that extend to areas of Downtown with residential areas; they are: Bruce Elementary School (in the Fifth Ward) Crockett Elementary School (northwest of Downtown) Gregory-Lincoln Education Center (in the Fourth Ward) Gregory Lincoln Education Center (in the