The Silver Line is a 2.7-mile (4.3 km) heritage streetcar line operated by the San Diego Trolley, an operating division of the San Diego Metropolitan Transit System. It currently operates the "downtown loop"; a circle of tracks around Downtown San Diego, and is operated using renovated historic vehicles. The line is also known as the SDG&E Silver Line after San Diego Gas & Electric (SDG&E), which has provided grants to help restore the streetcars and also sponsors a 3rd-grade history curriculum that includes free rides on the line. The line is one of four lines in the Trolley system; the others include the Blue, Orange, and Green lines.