Above Boston’s highways and railroad tracks are acres of space that, with proper planning and execution, could be utilized to construct transit-oriented, environmentally-sustainable development projects in core neighborhoods that would provide our economy with much-needed housing and innovation space, in addition to funding for transportation improvements and expansions. Across the United States, including here in Boston, developers and municipalities are capitalizing upon airspace over existing properties and rights-of-way and building transformative development projects that are knitting together long-severed urban fabrics and providing cities with the space they need to grow.

Hudson Yards in New York City, a 28-acre mixed-use air-rights development over an active rail yard.

In Boston, a number of key projects have been built over highways and railroad tracks owned by the Massachusetts Department of Transportation (MassDOT) and Massachusetts Bay Transportation Authority (MBTA). The Prudential Center, one of Boston’s major landmark structures and the city’s second-tallest building at 750 feet high, was built over a former Boston and Albany Railroad yard in the 1950s and today stands atop the Massachusetts Turnpike. Likewise, the Copley Place office, retail and hotel development in Copley Square, the last air rights development to be completed in Boston over 30 years ago, is built over the Massachusetts Turnpike, as are the Hynes Convention Center and the parking garage at 100 Clarendon Street.

Copley Place, as seen from Copley Square. 

In New York City, many new skyscrapers are built by buying the air rights of neighboring shorter buildings, which can be controversial as well as a windfall. Last Summer here in Boston, developer New Boston Ventures acquired air rights for its’ new 12-story Boulevard on the Greenway mixed-use development in the Financial District from the Boston Planning & Development Agency (BPDA), given that a number of residences at Boulevard on the Greenway’s edges will extend into public right-of-way, namely the surrounding streets. Boulevard on the Greenway will feature 36 condominium residences with ground-floor retail.

Boulevard on the Greenway, as seen from the Greenway. 

Air rights development over the Massachusetts Turnpike has seen a resurgence over the past few years, with a number of new projects in the pipeline. Across from Copley Place, the Back Bay/South End Gateway project, a 1.26-million-square-foot development, is proposed to be constructed above the Back Bay train station and adjacent parking garage. The development would include approximately 575,000 square feet of office space, approximately 100,000 square feet of retail space and approximately 600 residential units, and would also fund improvements to Back Bay Station.

The Back Bay/South End Gateway project, as seen from Southwest Corridor Park. 

Viola Back Bay, a 390,000-square-foot hotel and residential building, is slated to be built over the Massachusetts Turnpike at the intersection of Boylston Street and Massachusetts Avenue. The building will feature a 156-room hotel, 88 condominiums and 85 apartments, and will also modernize the adjacent Hynes Convention Center MBTA Green Line station.

The Viola Back Bay is a 390,000 square foot building slated to be built over the Massachusetts Turnpike in Back Bay.

Across from The Viola, both 1000 Boylston Street, a two-tower, 689,000-square-foot residential and retail development, and a second mid-rise residential building are currently proposed. 1000 Boylston Street would feature a 40-story condominium tower with 160 residences and a 24-story apartment tower with 182 residences, both standing above 35,000 square feet of retail. The second mid-rise building is currently in its’ early planning stages; the mid-rise would be built at the site of Boylston Square, an abandoned air rights development proposal which would have constructed a 50-story, 1-million-square-foot tower with hotel and residential space, in addition to a movie theater.

The proposed mid-rise building at the intersection of Boylston Street and Massachusetts Avenue.

Aerial view of the proposed 1000 Boylston Street development. 

The former Boylston Square proposal.

Finally, Fenway Center, a 1.1 million square foot mixed-use air rights development project in Kenmore Square adjacent to the Yawkey commuter rail station, is expected to break ground by the end of this year. The project will consist of five new buildings, including a 27-story tower. A total of approximately 550 residential units, 160,000 square feet of office space and over 50,000 square feet of retail will be built at Fenway Center in addition to over 30,000 square feet of park and green space.

Aerial view of Fenway Center, which is expected to break ground by the end of 2017.

Air rights development over MBTA rights of way is on the rise as well. The South Station Air Rights project will construct multiple towers featuring one million square feet of residential, hotel and office space, and will also modernize and improve South Station. The project’s first phase, a 51-story, 677-foot tall, 1,032,000 square foot tower featuring office, residential and retail space, is slated to break ground by the end of 2017.

Phase One of the South Station air rights project, which will feature three towers and nearly two million square feet of development.

While there are numerous air rights development opportunities over MBTA property, there are a number of drawbacks to building atop active railways. One general concern is that a development over a rail yard would reduce the capacity of the yard. Another is that a yard servicing diesel locomotives or buses would have to be vented. According to Let’s Go LA, most rail yards don’t have enough space between tracks for all the support columns necessary for air rights development. Other issues include the necessity of having to avoid interrupting rail operations, which limits when and how much work can be done. Furthermore, the required decking over existing rights-of-way adds millions of dollars to project costs. However, Boston’s past success with development such as the Prudential Center, Copley Place, the Crowne Plaza Hotel in Newton and the Star Market in Newtonville points to the viability of air rights development and why such projects are still worth undertaking.

The Crowne Plaza Hotel in Newton, which is built above the Massachusetts Turnpike.

One of the largest potential Boston-area air rights development sites is around Wellington Station in Medford. There’s a surface parking lot of about eight or nine acres that could be built over. The MBTA would not have to give up parking revenue, and the Orange Line would be right there. The Wellington rail yard proper would be another good site for air rights. Such development could have excellent views of the Mystic River and Downtown Boston. Much like Assembly Square in Somerville, the area could be attractive to businesses looking for office space. Upon the yard’s original design in the late 1960s, the yard was actually designed to accommodate air rights development that was never built. Likewise, Oak Grove Station at the northern tip of the Orange Line also has a large parking lot that could be built over.

The Wellington rail yard.

The Orange Line south of Tufts Medical Center has good potential, too. The section of the Orange Line between Clarendon Street and Harrison Avenue, which parallels the Massachusetts Turnpike and commuter rail tracks, is ideal for air rights, particularly considering recent development in the Upper South End, for instance Ink Block, as well as the demand in Bay Village and the South End and existing amenities. Columbus Center, a 10-acre air rights project, was slated to be constructed over the Massachusetts Turnpike, commuter rail and Orange Line between Clarendon and Arlington Streets but ultimately fell victim to the economic downturn. At least two major developers, including Trinity Financial, are currently preliminarily interested in reviving Columbus Center.

A rendering of the original Columbus Center proposal.

Along the Southwest Corridor, both Ruggles Station and portions between Prentiss Street and Williams Street are also ripe for air rights development, featuring access to major roads and the Southwest Corridor Park. Further south, between McBride and New Washington Street, air rights development may be more difficult due to the lack of street frontage. At the southern tip of the Orange Line, Forest Hills Station, the MBTA owns the eight-acre Arborway Yard, which is currently used as a bus parking facility. The MBTA has previously proposed to build a bus depot and turn most of the site over to developers; however, such a transfer has not taken place.

Along the Blue Line, the Orient Heights rail yard stands out, not only for the housing potential but also because that yard is extremely vulnerable to flooding and an air rights podium could help protect it. The yard’s smaller size and narrowness may also make it attractive by potentially simplifying the air rights engineering.

At either end of the Red Line, there’s development potential with the parking garages at Alewife and Braintree. However, the best opportunity for air rights along the Red Line is Cabot Yard in South Boston. The yard effectively runs between South Station and Andrew Station; with such a large space, the proximity to Downtown Boston and the Seaport District and separation from the main area of contention in the neighborhood, and both Interstate 93 and an industrial area as buffers, there could be potential for a very large air rights project with plenty of height. The development could also include air rights over Interstate 93, bridging Andrew Square and South Bay.

A rendering of proposed air rights development at Widett Circle, part of Cabot Yard, which could have taken place following the Boston 2024 Olympics on decking built to accommodate the Olympic Stadium.

The Commuter Rail maintenance facility on the Cambridge/Somerville border has some potential. It’s near the North Point development and could have MBTA access via the Community College and Lechmere stations. Somerville has some interesting opportunities in the form of the commuter rail lines -- Fitchburg, Haverhill and Lowell Lines -- that run through it. The Haverhill and Lowell Lines are in a trench that will also be home to the Green Line Extension, making the area around its stations more in demand. Decking would have to be vented, and the trenches suffer from the same lack of street access as the Orange Line south of McBride Street. However, the Fitchburg Line runs directly alongside Somerville Avenue for part of its length, near Porter Square. Indeed, the MBTA has looked at selling air rights there twice before, in 2003 and 2011.

A past MBTA case study for air rights development near Porter Square.

Economics are the biggest challenge to air rights development. While air rights can often accomplish important urban planning goals, building decking over active facilities, whether rail, bus or highway, does not come cheap. A deck over Widett Circle, part of Cabot Yard, proposed for the Boston 2024 Olympics would have cost $1 billion alone. Because building them is so expensive, air rights projects frequently require tax rebates. Developers may also be unwilling to purchase or lease air rights at market rates due to the complications of building and the existing active infrastructure underneath. However, just because something is difficult, doesn’t mean it’s a bad idea or can’t be tried. Copley Place connected the South End and Back Bay neighborhoods for the first time, revitalizing the previously-neglected South End which also spurring important construction such as the Tent City affordable housing development. In the long term, air rights development can be a transformative impetus for positive advancement in cities, turning dividing factors such as highways into seamless transitions and new gateways.