Here's a riddle: When is a tax not a tax? When Acting Governor Jane Swift says so.

The Acting Governor, like her predecessors Bill Weld and Paul Cellucci, has staked her political future on opposition to new taxes, as long as she gets to define what is a tax.

The Acting Governor, however, again like her predecessors, cynically skirts her "principled" stand when the issue is tolls for North Shore commuters.

A toll, after all, is not a tax according to the Acting Governor.

Of course, almost everyone who has to pay to cross the Tobin Bridge or drive through the harbor tunnels would disagree with the Acting Governor's definition.

Even Webster's Dictionary disagrees with the Acting Governor. According to Webster's, a toll is defined as "a tax or a fee paid for some liberty or privilege."

No issue has exposed the cynicism of the Weld-Cellucci-Swift administration's position on toll increases more than the Big Dig.

In 1996, then Governor Weld pushed legislation to create the Metropolitan Highway System (MHS), effectively creating a funding source to cover the rocketing cost of the Big Dig.

The purpose of the Metropolitan Highway System was to place under a single managing agency, the roadways currently run by the Turnpike Authority and MassHighway, as well as the new roadways being built by the Central Artery and Harbor Tunnel Project in the Metropolitan Boston area.

The problem with that plan is that a disproportionate share of Big Dig costs fell on the shoulders of commuters from the North Shore. The end result was legislation that mandated major toll increases, in perpetuity, to pay for the Big Dig.

North Shore and Metro West commuters bear the brunt of the financial load under this plan through higher tolls on the Tobin Bridge, Harbor Tunnels, and Massachusetts Turnpike, while commuters from the South Shore and outside of Route 128 are held relatively harmless.

I actively opposed and voted against the plan in 1997 because of the unfair burden it placed upon my constituents.

The legislation was nothing more than a convenient method of financing the Big Dig, using a limited and disproportionate system of tolls.

Weld's successor, Paul Cellucci, inherited the Big Dig and his cynicism. During the 1998 gubernatorial campaign he repeatedly promised the project was "on time and on budget."

Three years later, we are now looking at $2 billion in cost overruns, with no guarantee that costs are stabilized.

Now, Governor Cellucci is our Ambassador to Canada, leaving Acting Governor Swift the problem of paying for the mismanagement of her predecessors.

In politics, however, problems provide opportunity for bold leadership.

Those of us who had served with Governor Swift had high hopes, knowing her to be intelligent and capable.

But instead of seizing the moment, the Acting Governor fell back on the tired "no new taxes" chant of her immediate predecessors.

Faced with declining revenues and a mandated payment for their share of Big Dig costs, the Massachusetts Port Authority and its politically appointed board are now considering increasing tolls on the Tobin Bridge.

Across-the-board toll hikes, which unfairly burden select residents, should no longer be seen as the quick and practical way to generate revenues.

My colleagues from the North Shore and Metro West are taking a stand, speaking loudly and clearly. The administration has failed to produce a broader-based plan to pay for the Big Dig.

Our concerns are with the future increases. The long range increases of 25% every six years are completely unacceptable. Our children do not deserve to pay for the failures of the current administration.

The legislature has an obligation to address the fairness question and explore more equitable sources of revenue.

The only real solution to eliminate the inequity dilemma is a broad-based gas tax.

A gas tax is a fair and reasonable alternative to pay for Big Dig cost overruns, instead of using tolls that affect only those who commute to Boston from the north or west.

In the Acting Governor's view, taxes and tolls are very different, despite the views of the North Shore commuters and the definition found in Webster's.

That is why she believes it is okay for her to raise tolls for North Shore commuters while commuters from the South Shore travel for free.