The Southeastern Pennsylvania Transportation Authority (SEPTA) is a metropolitan transportation authority that operates various forms of public transit—bus, subway and elevated rail, commuter rail, light rail and electric trolleybus—that serves 3.9 million people in and around Philadelphia, Pennsylvania, United States. SEPTA also manages construction projects that repair, replace, and expand infrastructure and rolling stock. SEPTA serves the combined city and county of Philadelphia, plus the suburban counties of Delaware, Montgomery, Bucks and Chester. SEPTA also serves New Castle County in the state of Delaware and Mercer County in the state of New Jersey. Unlike U.S. transit agencies of its comparable size that are a state-run agency operated as a leg of its corresponding transportation department, SEPTA is not a state agency and is beholden primarily to the five local Pennsylvania-based counties which comprise it. SEPTA has the 6th-largest U.S. rapid transit system by ridership, and the 5th largest overall transit system, with about 306.9 million annual unlinked trips. It controls 290 active stations, over of track, 2,295 revenue vehicles and 196 routes. SEPTA also manages Shared-Ride services in Philadelphia and ADA services across the region. These services are operated by third-party contractors. SEPTA is one of only two U.S. transit authorities that operates all of the five major types of transit vehicles: regional (commuter) rail trains, “heavy” rapid transit (subway/elevated) trains, light rail vehicles (trolleys), electric trolleybuses and motor buses. The other is Boston’s Massachusetts Bay Transportation Authority (which runs ferryboat service as well). SEPTA’s headquarters are located at 1234 Market Street in Center City, Philadelphia.