MBTA Weighing Options for Green Line Expansion Project

The board that oversees the Boston-area public transit system is weighing options for a key expansion project after learning it might cost much more to build than originally estimated.

The Massachusetts Bay Transportation Authority's control board plans to discuss the Green Line extension during a meeting on Wednesday.

The proposed 4.7 mile extension through Somerville and Medford was among several transit proposals the state agreed to in 1990 to help pave the way for the massive Big Dig highway project.

The long-delayed Green Line extension appeared to be back on track in January when the federal government committed nearly $1 billion to the project.

But its future was clouded again when MBTA officials later revealed the state's share of the cost could be up to $1 billion higher than expected.