Romney had twice sought control of the Massachusetts Turnpike Authority, which oversees the project, but was rebuffed by the Legislature, where the authority's chairman, former Republican state senator Matthew J. Amorello, had important friends.

It took a tragedy to bring change.

Crisis moment

On July 10, 2006, a ceiling panel fell on a car driving through a Big Dig tunnel, killing Milena Del Valle, a 38-year-old mother of three from Jamaica Plain. Three days later, the Legislature handed emergency powers to Romney and Amorello soon resigned.

After the accident, a fearful public wondered how safe the mega-project truly was. Romney stepped in, a commanding, reassuring presence. At press conferences, he demonstrated a mastery of complicated engineering details as he announced plans for inspections and repairs.

"At a moment of crisis, he exercised significant leadership," said David Luberoff, co-author of a book about the Big Dig and other mega-projects.

Many other observers say Romney was at his best in crisis mode, taking charge of an issue and seeing it through to resolution. At other times, though, Romney seemed conscious of little other than political image.

He embarked on a road trip to cities around the state to promote a 20-year transportation plan — an ambitious $31 billion blueprint to improve highways, expand rail lines and repair the state's aging infrastructure.

But more than a year later, as the plan underwent public hearings and revisions, a nonpartisan transportation finance commission identified an enormous funding gap, another $15 billion to $19 billion would be needed over 20 years just to fix existing infrastructure and clean up the financial mess at the state's deficit-ridden transportation agencies.

Stephen J. Silveira, a Republican Romney appointed to chair the commission, said he warned the governor about the funding gap.

"I said, 'Before you finalize it, I think you want to be aware of what it is we're seeing,"' Silveira recalled. "And he said, 'We're done with that. We put a plan out.' And that was it. ... It was an afternoon meeting, and it was literally as if he was telling me it's pitch black outside."

Romney faced complaints in other areas that he raised expectations on big initiatives before retreating to safer political ground.