Blue Line (San Diego Trolley)

The Blue Line (officially the UC San Diego Blue Line for sponsorship purposes) is a 26.3-mile (42.3 km) light rail line in the San Diego Trolley system, operated by San Diego Trolley, Inc., an operating division of the San Diego Metropolitan Transit System (MTS). With an end-to-end travel time of one hour and twenty-three minutes, it operates between UTC Transit Center and San Ysidro Transit Center, the latter of which is at the Mexico–United States border directly adjacent to the San Ysidro Port of Entry, facilitating easy connections across the border. The line serves La Jolla, downtown San Diego, National City, Chula Vista, and San Ysidro and is the system's longest line.

The Blue Line is one of five lines in the trolley system, along with the Orange, Green, Copper, and Silver ("heritage weekend" service only) lines. Among them, the Blue Line has the highest ridership, transporting 24,389,986 total riders, or 75,160 per day, in fiscal year 2024. Its sponsored name is due to a $30 million naming rights deal with UC San Diego Health. An extension to its namesake campus of the University of California, San Diego, as well as nine other stations, opened to revenue service on November 21, 2021.