The Silver Line is the only bus rapid transit (BRT) line currently operated by the Massachusetts Bay Transportation Authority (MBTA). It operates in two sections; the first runs from Dudley Square in Roxbury to downtown Boston, Massachusetts and South Station, mostly via Washington Street, with buses operating in reserved lanes. The second section runs from South Station to several points in South Boston and to Logan Airport in East Boston, partly in a dedicated bus tunnel and also on dedicated surface right-of-way. Riders can transfer between the sections at South Station; transfers there between SL1 and SL2 and the Red Line – but not SL4 – are within fare control. - timosha21 on YouTube.