Lines

Blue Line trains operate between Old Town and San Ysidro. The Blue Line serves Old Town, Middletown, Little Italy, Downtown San Diego, National City, Chula Vista, and Imperial Beach.
Green Line trains operate between Santee Town Center and Old Town. The Green Line serves Mission Valley, the College Area, El Cajon, and Santee.
Orange Line trains operate between Gillespie Field and the 12th & Impreial Transit Center. The Orange Line operates in a "loop" around most of Downtown San Diego. This line serves El Cajon, La Mesa, Lemon Grove, East Village, and Downtown San Diego.
Special Event Service trains operate between Qualcomm Stadium and the Gaslamp Quarter (within walking distance of Petco Park). This service only operates during Padres home games, and times when large crowds are expected at Petco Park, the Convention Center, or Qualcomm Stadium. Special Event trains do not tend to operate on a timetable, but are usually only about five minutes apart. The MTS's Special Event schedule is available here.

Stations and Destinations

Transit Centers offer connections to many bus routes serving the local area.
Major sports venues are home to the Chargers and the Padres.
County and Federal Courthouses are located between America Plaza and Civic Center/2nd & C. You can get off at either stop if you're a juror, for instance.