BOSTON (CBS) – The MBTA’s $2.3 billion Green Line extension project got a big boost from the federal government Tuesday.

The Federal Transit Administration approved the T’s revised cost estimate for the project to extend the line into Somerville and Medford.

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(WBZ-TV graphic)

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The MBTA was initially given a $1 billion federal grant for the five-mile extension, which would create seven new T stations.

But the sky-rocketing projected costs put the brakes on the proposal for a year.  That prompted the T to scale down the project. The revised version then had to be reviewed by the FTA in order to keep the grant.

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Once a design team is selected in the fall, work could begin on the extension next spring.