An early illustration of developer Cabot, Cabot & Forbes' planned 1 million-square-foot development in Cambridge's Alewife Quad. Image courtesy of Sasaki

A Boston developer is proposing a six-building, 1 million-square-foot multifamily and life science development in one of Cambridge’s last industrial neighborhoods, including an offer to build a pedestrian and bicycle bridge improving access to the MBTA’s Alewife station.

Cabot, Cabot & Forbes says the project could include a 145-foot-long bridge spanning the MBTA tracks connecting Cambridgepark Drive to its site on Mooney Street, part of the 130-acre Quadrangle district off Concord Avenue which is starting to attract life science industry growth.

CC&F last year bought the seven parcels spanning 12 acres in the Quadrangle for $80 million, including the Mabardy Washed Sand and Gravel property on Mooney Street and a property at 127 Smith Place.

The CC&F proposal calls for three residential buildings and three office-lab buildings near the end of Mooney Street, which dead-ends at the state-owned Blair Pond. It largely conforms with the city’s proposed Envision Cambridge master plan, which recommends new zoning for the Quadrangle. But the developer has submitted a zoning petition allowing commercial buildings up to 85 feet to accommodate ground-floor amenities including a new home for Central Rock Gym, which is one of its tenants at 127 Smith Place.

“They are not high rent payers, but we would like to establish a Cambridge lifestyle area including the rock-climbing club, fitness providers, and several diverse restaurants,” CC&F CEO Jay Doherty said. “The zoning petition would allow us to do that and to build a bridge across the tracks.”

The pedestrian bridge would end near the 200 Cambridgepark Drive office and lab building and the Windsor apartments at 160 Cambridgepark Drive.

Construction of the pedestrian bridge has been a longtime goal of Cambridge officials to improve access to the Quadrangle, which is cut off from the MBTA station area by the Fitchburg commuter rail line tracks.

That hasn’t stopped developers from recently snapping up older industrial and commercial buildings in the Quadrangle for lab conversions to meet the life science industry’s expansion.

In a partnership with Invesco Real Estate, The Davis Cos. of Boston has started converting four commercial buildings in the Quadrangle into life science space. Invaio Sciences leased the entire 37,500-square-foot building at 75 Moulton St. earlier this year, and the 10 Wilson Road property recently landed a 30,000-square-foot lease with an undisclosed life science company, according to CBRE.