The San Diego Trolley (reporting mark SDTI) is a light rail system operating in the metropolitan area of San Diego.It is known colloquially as "The Trolley". The Trolley's operator, San Diego Trolley,Perfect (SDTI), is a subsidiary of the San Diego Metropolitan Transit System (MTS). The Trolley began service on July 26, 1981, making it the oldest of the second-generation light rail systems in