BOSTON—In the waning days of 2015, Boston Properties announced that it would be submitting plans in early 2016 for a major mixed-use project in the city's Back Bay.

The commercial developer filed a letter of intent with the Boston Redevelopment Authority on Dec. 29 for the development of four air and ground leased parcels at 145 and 165 Dartmouth St. The plan for the properties that are to include parcels in and over the existing parking garage at 165 Dartmouth St. and Back Bay Station at 145 Dartmouth St. calls for approximately 1.4 million square feet of mixed-use development.

MassDOT approved the long-term leases of the four air and ground parcels on Dartmouth St, to Boston Properties in December 2014. Boston Properties expects to spend approximately $32 million on renovations to the Bay Back Station and Concourse in exchange for the ground and air rights leases, according to a report in the Boston Globe. According to minutes from the MassDOT Board of Directors meeting on Nov. 14, 2014 that authorized the negotiation of the Back Bay term sheet with Boston Properties, the deal would allow the development of up to three additional buildings at the property that is bounded by Dartmouth, Stuart and Clarendon streets and Columbus Avenue.