State Rep. Denise Provost (D-Somerville) posted on her Facebook page:

Early today, I was extremely disheartened to learn from MassDOT that the expected completion of the Green Line Extension has been delayed again – this time until at least 2018. While I appreciate MassDOT’s efforts in appropriate mitigation and community input, I am extremely disappointed that this vital project is, yet again, being postponed. ...

In a statement, MassDOT says:

Over the past four months, the Green Line Extension project team performed a cost and schedule analysis that thoroughly examined all aspects of the project and the actions required to move it forward expeditiously. As a result of this analysis, the projections for the Green Line Extension project have been refined. Under the revised timeframe, passenger service would begin no earlier than the fall of 2018 and no later than the summer of 2020. The schedule is contingent on the MBTA taking full ownership of property required for construction. Benefitting from lessons learned on the Greenbush Commuter Rail project, in which the MBTA did not take ownership of needed properties until after the Design/Build process began, the Green Line project team aims to prevent the issues that cost the MBTA both time and money.

Seeking to accelerate the timeline where possible, MassDOT and the MBTA are actively considering strategies that could mitigate schedule impacts and improve upon the dates for passenger service on the Green Line Extension. The strategies under consideration include the development of a 'phasing' scenario that would allow for some stations to open for public use while others are still being constructed.