A real estate developer is taking steps toward redeveloping a Boston parking garage into an office tower, a project with the potential to not only make a portion of the Back Bay more attractive architecturally, but could also transform a major city intersection that sits at a crossroads of the Massachusetts Turnpike and the MBTA.

Major commercial property owner Boston Properties is starting down the long road to building a new office tower on the site of the hulking 2,000-car garage at 100 Clarendon St. in the city’s Back Bay neighborhood.

It is unclear if the developer would completely replace the garage, which it acquired when it purchased the John Hancock Tower in 2009. The parking facility spans an entire city block from Clarendon to Dartmouth streets above the Massachusetts Turnpike and sits adjacent to the Back Bay MBTA station with its confluence of subway cars, buses and commuter trains.

Boston Properties has not yet filed official plans with the Boston Redevelopment Authority (BRA), the agency in charge of land use within the city limits. But the property owner has discussed preliminary plans for an office tower with ground-floor retail at the site with BRA officials, according to business executives familiar with the proceedings. For their part, Melina Schuler, spokesperson for the BRA, wrote in an email that she did not “have any info” on the topic.  Boston Properties officials did not return calls seeking comment.

In The Process

While it is still early in the process, some are facts known about any potential development at the site. About a third of the garage’s footprint is atop actual terra firma; the remainder sits above the Massachusetts Turnpike. If a project were built above the Pike, the developer would need to build very expensive decking strong enough to support a big office building.

But “big” would likely be an understatement. According to one development consultant that works on similar projects in the city who asked for anonymity, the office tower would probably need to be upwards of 40 stories tall to house the number of tenants needed for the rent to support the project’s cost, especially if the entire garage were demolished and that revenue lost.

Those kinds of “air rights” projects above Turnpike are not always welcomed with open arms, especially in the Back Bay. Just ask anyone that watched the WinnCompanies’ failed attempt to push the Columbus Center mega-development air rights project through the local review process. Columbus Center would have spanned the Turnpike adjacent to where Boston Properties wants to build the office tower.

Plus, the proposed project would be immediately adjacent to another project in the works known as 40 Trinity Place. That development would bring a 33-story hotel and residential tower on the site of the former John Hancock Hotel & Conference Center on Stuart Street.

But Boston Properties is no stranger to the neighborhood. The firm already owns the Hancock Tower and the Prudential Center and tower, along with the skyscrapers at 111 and 101 Huntington Ave.

There are a few things that could win over local support however. Back Bay residents have long bemoaned the lack of a westbound on-ramp to the Pike, especially since an eastbound exit dumps cars into the neighborhood near the Back Bay MBTA station.

“It’s a great opportunity for the neighborhood to solve some intrinsic issues, especially the Mass Pike ramp situation,” said Meg Mainzer-Cohen, executive director of the Back Bay Association, a business advocacy group. “When you walk down Clarendon Street and go from Stuart Street to Columbus Avenue, right now you passby some Mass Pike ramps, then big garage door openings, then you’re walking by a turnaround for the MBTA buses. Maybe there could be some new thinking brought to bear on that block that would improve it, all the while creating new office space or retail and activating the street wall. It’s really the beginning of a transition between the Back Bay and the South End, so to have an experience that better knits that together and better represents both neighborhoods, I think would be a positive thing.”

Email: jcronin@thewarrengroup.com