Original plans for the connector in 1986 called for a cut-and-cover tunnel extension west from Bowdoin, with an underground stub-end terminal connected to the existing Charles/MGH station. Three configurations for the Blue Line level at Charles/MGH were considered: a three-track terminal with two island platforms, a two-track terminal with one island platform and pocket tracks to the east, and a three-track terminal with one island platform (one track not used for passenger service) and pocket tracks to the east. The 2010 Draft Environmental Impact Report instead called for a pair of deeper tunnels bored by a tunnel boring machine (TBM); the Charles/MGH terminal would have a single island platform with tail tracks extended to the west.