When the Tremont Street subway fully opened in 1898, surface cars entering the subway from East Cambridge had to cross Craigie's Bridge and proceed on surface streets to the Canal Street incline. The trip from Lechmere Point over the bridge was slow and prone to delays. On June 20, 1907, construction began on one mile of elevated track connecting the Canal Street incline to East Cambridge. The project's centerpiece was the arched viaduct crossing the Charles River, with 12 spans including a short drawbridge section. Other sections of elevated track included the Causeway Street Elevated on the Boston side of the river, and the Lechmere Elevated on the East Cambridge side. The first streetcars crossed the bridge in revenue service on June 1, 1912, shortening the ten-minute trip from Lechmere Square to the subway to just three minutes. The building of the massive structure was done entirely by the Boston Elevated Railway, without use of subcontractors. The BERy opened Lechmere station on July 10, 1922, as a transfer point between the Cambridge streetcars and the subway cars. This prevented traffic delays affecting the surface cars from propagating into the subway, and allowed the underground service to use three-car trains, which were too long for safe street-running. On August 20, 1955, Science Park station opened as an infill station on the viaduct over Leverett Circle. It serves the Boston Museum of Science and the West End.
Service disruptions
On June 25, 2004, service over the viaduct was suspended as the Causeway Street Elevated was removed, and the surface and elevated platforms at North Station were consolidated into a new underground "superstation". This left the Lechmere Viaduct and Lechmere Elevated as the sole remaining elevated lines in Boston. A new portal was built off Martha Road, with a new concrete bridge connecting to the viaduct just south of Science Park station. Service to Lechmere resumed on November 12, 2005. The incline from the 2005-built tunnel to the Lechmere Viaduct is the steepest grade on the entire MBTA subway system. The viaduct was again closed from April 30 to November 4, 2011, as Science Park station was rebuilt with handicapped-accessible platforms and new elevators. As part of the Green Line Extension project, the northern section of the Lechmere Elevated will be removed and connected to a new elevated structure east of Route 28. The original Lechmere terminal will be replaced with a new elevated station to the east. The work requires closing the viaduct from May 24, 2020 to April 2021. Demolition of the northern section of the Lechmere Viaduct began on June 6, 2020. Only the steel section of the viaduct north of the Gilmore Bridge is being replaced; the main concrete span is being restored to support Green Line Extension service and future Type 10 vehicles. Only the E branch service used the viaduct; the B, C, and D branches terminated in downtown Boston. When the Green Line Extension is complete, the D and E branches will run across the viaduct: the D branch to, and the E branch to.
