On March 23, 1986, SDTI opened an extension east from Centre City San Diego to Euclid Avenue, along the La Mesa Branch of the SD&AE Railway – this new second line of the Trolley was then called the East Line.
with the inauguration of the third line of the San Diego Trolley system, the Green Line.
The planning for the San Diego Trolley began in 1966 under the auspices of the Comprehensive Planning Organization (CPO), an intergovernmental agency of 13 cities and San Diego County.
Although its operating names have changed over the years, the two modes of transportation, buses and trolleys, have remained consistent over the past 125 years.
San Diego Trolley initially used the same German-built Siemens–Duewag U2 vehicles as the Edmonton Light Rail Transit system in Edmonton and the C-Train in Calgary, Alberta, Canada, and the Frankfurt U-Bahn in Frankfurt, Germany.
The fleet has since been expanded to include Siemens SD-100 vehicles, and most recently Siemens S70 vehicles manufactured by Siemens.
when the Metropolitan Transit Development Board (now operating as MTS) began planning a light-rail service along the Main Line of the San Diego and Arizona Eastern Railway (SD&AE Railway), which had been purchased by MTDB from Southern Pacific Railroad in 1979.
In 1966 the local bus company, San Diego Transit, was facing a financial crisis and public takeover.
The CPO developed a mass-transit plan to address the long-range transportation issues of the metropolitan area. CPO continued to research options for addressing the region's transportation needs.
Several prominent stakeholders submitted their own mass-transit master plans for the region.
The San Diego Trolley (reporting mark SDTI) is a light rail system operating in the metropolitan area of San Diego. The entire Trolley network serves 53 stations, and comprises 53.5 miles (86.1 km) of route, and three primary lines named the Blue Line, the Orange Line, and the Green Line, as well as a supplementary heritage streetcar downtown circulator known as the Silver Line that operates on select weekdays, weekends and holidays.
(SDTI), making it the oldest of the "second generation" light rail systems in the United States.