Various extensions and branches were added to the subway lines at both ends, bypassing more surface tracks. As grade-separated lines were extended, street-running lines were cut back for faster downtown service. The last elevated heavy rail or "El" inter-station segments in Boston – with the exception of the Red Line's still-active elevated tracks, connecting Charles/MGH station over Charles Circle to the Longfellow Bridge and the Cambridge Tunnel's northern portal – were at the extremities of the Orange Line: its northern end was relocated in 1975 from Everett to Malden, MA, and its southern end was relocated into the Southwest Corridor in 1987. However, the Green Line's Causeway Street Elevated remained in service until 2004, when it was relocated into a tunnel with an incline to reconnect to the Lechmere Viaduct. The Lechmere Viaduct and a short section of steel-framed elevated at its northern end remain in service, though the elevated section will be cut back slightly and connected to a northwards viaduct extension in 2017 as part of the Green Line Extension.