San Diego Trolley

The San Diego Trolley is a light rail system serving San Diego County, California. The trolley's operator, San Diego Trolley, Inc. (reporting mark SDTI), is a subsidiary of the San Diego Metropolitan Transit System (MTS). The trolley operates as a critical component of MTS, with connections to and integrated travel tickets with the local bus systems.

The trolley system serves 62 stations, over about 67.9 miles (109.3 km) of route, using four primary lines (Blue, Orange, Green, and Copper) that operate daily, and a "downtown loop" heritage streetcar line (Silver) that operates on holidays. There is one downtown station where all major lines connect, and thirteen other stations that provide transfers to a second line (two of these also provide connections to commuter rail systems).

The trolley began service on July 26, 1981, making it the oldest of the second-generation light rail systems in the United States, and the success of the system helped spark a nationwide revival of light rail. In 2024, the trolley had the second-highest ridership of any light rail system in the United States, with 38,047,300 annual rides, or about 122,000 per weekday as of the first quarter of 2025.