Image courtesy Elkus Manfredi Architects

A $700 million development on a landmark Massachusetts Turnpike air rights parcel is beginning construction in Back Bay in spite of the uncertainties swirling around future demand for office, hotel and retail space.

Samuels & Assoc. has received construction financing for the $700 million parcel 12 project at the end of Newbury Street, which will bring Cambridge-based online marketplace CarGurus to Boston as anchor tenant of a 435,000-square-foot office tower. Dutch hotel chain citizenM will operate the 150,000-square-foot hotel, in a project that includes 50,000 square feet of retail space and a new public plaza overlooking the Turnpike.

Branded as 1001 Boylston, the project includes a new headhouse for the MBTA’s Hynes station on the western side of Massachusetts Avenue and separate zones for bike lanes, pedestrians and bus operations.

The project is a milestone in the Massachusetts Department of Transportation’s longtime attempts to generate revenue from a series of air rights parcels above the Turnpike in Back Bay and South End. MassDOT named Samuels & Assoc. as developer of parcel 12 in 2013.

Along with the high costs and complexities associated with construction above an active highway and rail lines, the project will reshape a landmark intersection and change how riders access MBTA bus routes and the Green Line.

Architects redesigned the original plans last year, moving the office and hotel buildings further apart, which preserved some of the westbound views from Newbury Street while enabling a larger portion of the buildings to be built on terra firma.

The ramp from Massachusetts Avenue to the westbound Turnpike will be relocated slightly north of its current location, making room for approximately one-half acre of public open space on the 1.8-acre site.

“Not only will it repair the scar created when the Mass Pike was constructed, it will establish the largest new public open space in the area in many decades,” Chairman Steve Samuels said in a statement. “In addition, the elegant architecture creates a new western edge of the Back Bay that is now visible when traveling east on the I-90.”

A New York developer is pursuing air rights plans for another nearby MassDOT parcel. Peebles Corp. is seeking Boston Planning and Development Agency approval for a 432,000-square-foot hotel and condo building on parcel 13, a 1.25-acre site on Boylston Street just east of Massachusetts Avenue.

Another developer, Boston-based Weiner Ventures, dropped plans for an $800 million condo tower near the intersection of Boylston Street and Massachusetts Avenue last year, prompting construction giant Suffolk to file a $100 million lawsuit alleging “gross mismanagement” of the project.