Boston Mayor Thomas M. Menino may have finally met his match, and I am not talking about a certain trash talking New York developer behind the Filene’s fiasco.

Rather, as the mayor pushes corporate expansion in hopes of generating thousands of new jobs, his ambitious agenda is poised to run headlong into a 1970s-era cap on the number of downtown parking spaces.

Menino and his capable crew at City Hall have managed to keep Boston’s skyline growing for years despite the cap, finding ways to stay under the mandated number of spaces.

But the days of creative solutions may soon be coming to an end. Boston’s already notoriously tight downtown parking situation is finally nearing the breaking point – potentially stifling new corporate growth in the downtown office market at one of the most challenging times in the Hub’s long history.

Leading the pack is a budding proposal by the Massachusetts Convention Center Authority to expand a parking garage under Boston Common, which could use up all the remaining downtown parking spaces still left under the cap, creating problems for future development, according to a recent report in the Boston Courant (in the interest of full disclosure, a report I wrote).

“At some point in time, you start to run into the wall,” said David Begelfer, CEO of commercial development association NAIOP. “The wall is where you run out of these spaces that are required for future growth.”

“You take a look at where we are and where we are going and you realize we have serious problems looming in the near future,” he added.

Deal With The Devil

The culprit here is a top down, Soviet-style bid to save the environment by punishing commuters who drive to work.

In order to comply with the federal Clean Air Act, Boston in the Kevin White years of the 1970s, capped the number of commercial parking spaces allowed downtown.

By limiting the number of garage and lot spaces to 35,576, backers of the freeze argued it would force people out of their cars and into trains.

“The city made a pact with the devil to deal with this Clean Air Act, and now it’s coming due,” Begelfer warned.

Of course, we know what really happened. The number of cars on the road in Greater Boston has grown exponentially as companies have pushed out from downtown, building sprawling new complexes in the suburbs.

Still, thanks to creative parking cap juggling by city bureaucrats, Boston was able to keep adding to its bejeweled skyline, with the downtown office market growing through the 1980s, 1990s and 2000s.

But the Hub’s luck may finally be running out, with the parking freeze rearing its ugly head just as Menino and City Hall scramble to shore up the downtown office market and keep companies from bolting for the suburbs.

Menino just unveiled a deal to shower millions in tax incentives on Liberty Mutual as part of an agreement that will see the big insurer expand its downtown headquarters.

The move, if anything, was a preemptive strike, with Liberty courted aggressively by suburban locales interested in gaining well-paying jobs and oodles of real estate taxes.

But keeping additional companies anchored downtown – and enticing developers to build new towers as well – could prove increasingly difficult under the growing tyranny of the parking cap.

Zero Sum Game

For starters, the Massachusetts Convention Center Authority is seriously exploring plans to double the size of the garage it owns underneath Boston Common.

That could add another 1,300 spaces to the Boston Common Garage, eating up all of the remaining 800 downtown parking spaces still left under the cap, and then some.

“Certainly if they do expand the Common garage they will exhaust all the spaces,” said former Boston City Council President Larry DiCara, now a partner at NixonPeabody specializing in real estate. “It’s a zero sum game.”

Sure, maybe more parking spaces in the Common garage will help support additional office development downtown. But for the secretaries and back office workers who will end up using the garage, it is a hike, especially on cold winter mornings, to either the Financial District or the Back Bay.

Still, it is sure to at least serve one purpose – generating millions for the state convention center authority, which is also weighing an ambitious expansion of the Boston Convention and Exhibition Center down in South Boston.

But an even greater long-term threat to the precarious downtown parking situation looms as well.

Downtown Boston has been able to survive all these years under the parking freeze because it sits next door to acres upon acres of surface parking lots along the South Boston waterfront.

Those lots, which don’t fall under the downtown cap, have acted as a safety valve over the years for the Financial District, providing ample and fairly cheap spaces to commuters.

But demand for those spaces is already rising, with two nearby office high-rises, at Fan Pier and Russia Wharf, preparing to open.

More importantly, local developer John Hynes and investment backer Morgan Stanley plan to convert most of the waterfront’s remaining surface lots into condos, stores and offices.

And when that happens, all bets are off.

Maybe, as all the environmental purists have long hoped, Boston’s legions of office workers, no longer able find a parking space in the city, will dump their cars and head to the commuter rail station, laughing off the more-than-occasional no-show train and schedules that are rarely kept.

But my guess is that instead, we’ll get more companies leaving Boston and heading to the suburbs, building bigger and better office complexes, and dumping more traffic on roads that were previously secondary backwaters.

And no, you still won’t be able to find a parking space downtown.