The MBTA will extend Silver Line bus service to East Boston and Chelsea by late 2015, connecting the neighborhoods to Logan Airport, the Seaport District and South Station, Gov. Deval Patrick's office announced Wednesday morning.

The $82.5 million project, called the Silver Line Gateway Expansion, will create Silver Line stations at Eastern Avenue, Chelsea's Box District, Downtown Chelsea and the Mystic Mall.

The MBTA estimates travel time between the Seaport District and Chelsea will be 15 to 19 minutes, and it projects as many as 9,000 people will ride the new line daily.

"Bringing Silver Line service to Chelsea will provide an even more convenient and cost-effective route for its residents and neighbors to connect with the vibrant opportunity growing in the Seaport District and the City of Boston," Massachusetts Transportation Secretary Richard Davey said in a statement.

The most expensive part of the project will be a $20 million expansion of the Chelsea commuter rail station, which will be relocated to Everett Avenue.

Patrick also announced a $3 million state investment in the Chelsea Greenway, a three-quarter-mile green space which will run along a section of former railroad tracks. It will provide a walking and cycling path between the Box District and Bellingham Hill neighborhoods.