The San Diego Trolley 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, Inc. (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 the United States. The Trolley system serves 62 stations, comprises of route, three primary lines (Blue Line, Orange Line, and Green Line) that operate daily, and one heritage line (Silver Line) that operates on a circuit of downtown on select days. In , the Trolley had the fifth highest ridership of light rail systems in the United States, with annual rides, or about per weekday as of . History Early history Electric rail service in San Diego traces its roots back to 1891 when John D. Spreckels incorporated the San Diego Electric Railway. San Diego's streetcar system had been replaced with buses in 1949, and by 1966 the local bus company, San Diego Transit, was facing a financial crisis and public takeover. Planning for mass transit in the San Diego region began in 1966 under the auspices of the Comprehensive Planning Organization (CPO, now known as the San Diego Association of Governments, SANDAG), an intergovernmental agency of 13 cities and San Diego County. Over the next decade, the CPO researched various technologies were studied including improvements to local buses, express buses, heavy rail, light rail, and advanced technologies. The CPO also closely studied the San Francisco Bay Area Rapid Transit (BART) system, then under construction. Ultimately, the early studies went nowhere due to disagreements between stakeholders and a lack of funding. In 1975, the CPO published the Regional Transportation Plan which included intermediate capacity fixed guideway system (an untested technology at the time) at a cost of $1.5 billion. Metropolitan Transit Development Board In the early 1970s, three state legislative acts would set the stage for the construction of mass transit in the San Diego region. Transportation Development Act, signed by Gov. Ronald Reagan in 1971, earmarked 0.25 percent of the state sales tax for funding transportation projects, including mass transit. A 1974 amendment to Article 19 of the Constitution of California permitted the use of gas tax revenues, previously reserved for highway construction, for construction of rail systems. Finally, a 1975 law established the San Diego Metropolitan