U.S. Transportation Secretary Anthony Foxx yesterday joined Gov. Deval Patrick and other Bay State officials to formally announce a $996 million federal grant to extend Massachusetts Bay Transportation Authority (MBTA) Green Line light rail service from East Cambridge to Somerville and Medford.

The Federal Transit Authority announced its intention to provide nearly $1 billion for the $2.3 billion project in December. State funds will cover the remaining cost.

Acting Federal Transit Administrator Therese McMillan, Sen. Elizabeth Warren, Congressman Michael Capuano as well as representatives from the Massachusetts Department of Transportation and MBTA also attended the announcement at Somerville High School.

The 4.7-mile light rail extension will extend existing MBTA Green Line service from a relocated Lechmere Station in East Cambridge to Union Square in Somerville and College Avenue in Medford. The project will serve some of the Boston region’s most heavily populated areas where 26 percent of residents do not own or have access to cars.

The MBTA estimates the extended light rail line will provide approximately 37,900 daily trips when it opens in 2021. The project will include construction of six new stations, purchase of 24 new light rail vehicles, construction of a new vehicle maintenance facility, construction of a community bicycle and pedestrian path in Somerville and relocation of some existing commuter rail track.

"This project will put time back in the lives of commuters along this corridor, but the real story is about the potential for change this smart investment will bring for residents," Foxx said in a statement. "We are proud to support projects like this one because when you connect people to more jobs, education, and medical care, you create the ladders to opportunity that strengthen families and the communities in which they live."