The Silver Line is a bus rapid transit service on the MBTA. It consists of two parts: Waterfront and Washington Street, both split up into multiple lines. The Washington Street portion is meant to replace the old elevated train tracks over Washington Street. It has its own bus lane for most of the trip. The other portion is the Waterfront, which consists of an underground transitway with three stations. It then goes above ground and changes from electric to diesel power. Once above ground, it splits into two routes.