For the first time in four decades, new buildings could rise over the Mass. Pike

A rendering of the proposed towers as seen from the Mass. Pike. looking east.Elkus Manfredi

Central Boston unfolds east to west through the Back Bay one lively block after another before ending in a forlorn and windswept dead zone at Massachusetts Avenue. Now, this gritty stretch could be transformed if developers can pull off something no one has managed to do in four decades: Build above the Massachusetts Turnpike.

The development firm Samuels & Associates hopes to start work early next year on a major redevelopment of the west side of Mass. Ave. between Boylston and Newbury streets, where one of Boston’s busiest thoroughfares crosses the Pike and commuter rail tracks below.

Samuels plans to dramatically change the intersection with a pair of buildings and a two-level, half-acre plaza between them — all built on a deck above the highway. The complicated “air rights” project, seven years in the making, won a key vote from the Boston Planning & Development Agency on Thursday and now heads to the final stages of planning with state transportation officials.

“We’re looking forward to getting started,” said Peter Sougarides, a principal at Samuels & Associates, the prominent Fenway developer behind the project. If the company can begin construction next year, the $650 million complex could be finished by late 2022.

The Samuels buildings, along with two other long-planned air rights projects nearby, could help close over a hole carved by the highway between the Back Bay and Fenway. Samuels would put a 20-story office tower on the corner of Boylston Street and a 13-story hotel on the Newbury side — more than 600,000 square feet of space in all.

Between the two buildings would be an elaborate two-story public plaza with views west, out over the turnpike and to Kenmore Square and Fenway Park. The plaza would include a new entrance to the MBTA’s Hynes Convention Center Station, wider sidewalks, and bike and bus lanes for all the people that stream through this busy section of the city.

“You have this confluence of cars, bikes, buses, trains below . . . pedestrians, and having to figure out safe traffic patterns for everyone,” Sougarides said.

Traffic flow was a key point of discussion during the BPDA review process over the last year and a half. Another concern was open space. Samuels adjusted its original plan to include the plaza, one of several approaches that should improve the feel of what can sometimes be a harrowing place to walk.

A few residents of neighboring buildings remain concerned about the size of the project: The office tower will be nearly 300 feet tall, and the hotel 159 feet. But an array of Back Bay neighborhood groups and officials showed support for it in comment letters and at a public hearing Thursday, with several citing a more pleasant environment for pedestrians.

“It will turn our neighborhood from a sort of awful place into a marvelous place,” said Parker James, a longtime resident of the nearby Charlesgate section of the Back Bay, at Thursday’s hearing.

A rendering of the view from the bleachers of the Boylston Street development.Elkus Manfredi

The Samuels project is the largest of three so-called air rights developments proposed for above the Pike in that part of the Back Bay. But the slow progress of the others highlights how hard they are to actually launch.

Veteran development firm Weiner Ventures was approved last year to build a condo tower above the Pike at the corner of Boylston and Dalton streets, but a spokeswoman said Friday they have scrapped those plans, citing “a combination of factors.”

“While disappointing to have to make such a decision, we believe it is the correct one, and still paves the way for other future air rights projects to come to fruition,” the company said in a statement.

A hotel long planned across Mass. Ave. from Samuels’ site has also been dormant for several years. And a half-mile west down the Turnpike, developers John Rosenthal and Gerding Edlen are at work on the first phase of the long-awaited Fenway Center project, a pair of apartment buildings alongside the highway and Beacon Street, but are still planning a second phase that would actually span the highway.

Engineering and economic challenges of building above the highway and a busy commuter rail line are many, and a major reason nothing has been built above the Turnpike since Copley Place in the early 1980s, despite several attempts.

Samuels executive Abe Menzin said the company has spent years working on the engineering of building over the highway and is in “very advanced” stages of planning. Samuels is confident it can begin construction next year, he added.

A spokeswoman for the Massachusetts Department of Transportation said the agency and Samuels will finalize permits and a lease for the site, and “make decisions about a schedule for construction, which will be closely coordinated and sequenced with other projects being built in the Back Bay and Allston neighborhoods.”

The timing could also be influenced by Samuels’ ability to sign tenants for the office building. Boston developers are often wary to launch construction without leases in hand, though several, citing the hot office market right now, have done so lately. Sougarides said no decision has been made, but he believes there is strong demand for new office space in the Back Bay.

“We’re very bullish on the office market,” he said. “There are a lot of tenants who have needs for this kind of building, in terms of size, location, etc. It’s a very tight market right now.”