In October 1936, construction of the subway to just shy of West Newton Street was approved as a WPA project. Work was expected to last 1 year and cost $1.715 million, with the city's share about $539,000. The Boston City Council and Boston Elevated Railway approved the plans in April 1937. Construction began on September 18, 1937. In 1938, the Boston Transit Department extended the project to Opera Place, with underground stations at and and an auto underpass of Massachusetts Avenue adjacent to Symphony station. The subway was constructed as twin tubes some long; they were adjacent except at Symphony station, where they ran on opposite sides of the underpass. The final cost of the project was $7.13 million (equivalent to $ in ), of which the city paid $1.93 million and the federal government $5.20 million.