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Massachusetts Turnpike Authority Chairman Matthew Amorello, under fire since heavy ceiling panels in a Big Dig tunnel collapsed on a motorist, agreed Thursday to resign after weeks of pressure on him to step aside.

Amorello's resignation will be effective Aug. 15, but he will continue to receive his $223,000 annual salary through Feb. 15. He will leave the board completely, not just step down as chairman and chief executive.

He announced his decision an hour before a scheduled hearing in the governor's office during which Gov. Mitt Romney planned to seek his removal. He lost a bid in the state's highest court Wednesday to postpone the hearing and his ultimate dismissal.

"I think this is good news for the commonwealth, the right step for Matt Amorello to have taken," Romney said. "Clearly it will save the taxpayers and the rate-payers the cost of an extensive legal battle, and it also allows the citizens and toll-payers to have confidence again in the Turnpike Authority and new leadership that will be installed."

Amorello's resignation comes after months of pressure from Romney, a fellow Republican, that has intensified since July 10, when 12 tons of ceiling panels fell from a Big Dig tunnel, crushing a car and killing its passenger, Milena Del Valle, 39, of Boston, and injuring her husband, Angel, 46.

Lawyers for Amorello and Romney hammered out details of his resignation late Wednesday, after Supreme Judicial Court Justice Francis X. Spina ruled Romney could go forward with the administrative process to remove Amorello. A lawyer representing Amorello delivered the signed agreement to the Governor's Office Thursday morning.

Under the terms of the agreement, a copy of which was obtained by The Associated Press, Amorello will get just over two weeks to clean out his office. Although he will get paid through February, the deal is less generous than one proposed by House and Senate leaders two weeks ago; that called for him to get his full salary through July 1, 2007.

In addition, the agreement requires that he call a board meeting for Aug. 16, the day after he departs, with an agenda set by the Romney-nominated board majority.

The agreement also would make Amorello personally responsible for reimbursing the state if he were to be found to have not acted lawfully or in good faith in ongoing federal and state probes. At the board's most recent meeting, Amorello had pushed through more generous protections for himself personally.

Most importantly for Amorello, however, may have been the fact that in signing the agreement, he avoided Thursday's hearing, during which he would have been deposed — under oath — at a time when both federal and state officials are conducting criminal investigations of the accident. That would have created a legal record that investigators could have used as part of any case alleging criminal activity.

In speaking with reporters, Romney reiterated his plans to launch a nationwide search for a new leader of the Turnpike Authority who won't come out of the political arena but instead has relevant transportation experience. He said he did not have anyone specific in mind and had no timetable.

Amorello, 48, a former state senator and failed congressional candidate who served as Massachusetts Highway Commissioner, was appointed to head the Turnpike in February 2002 by Romney's predecessor, acting Gov. Jane Swift.

Since that time, he has shepherded the highway project through the final phases of construction while maintaining its cost at an estimated $14.625 billion. However, he has faced consistent criticism for an imperial manner, preferring to be called "Mr. Chairman," holding meetings at early-morning hours and in distant locations, and clashing with critics of his management style.

Though Amorello's job involves overseeing the 138-mile Mass Pike, which stretches from Stockbridge to Boston's Logan International Airport, his primary responsibility is for the Big Dig.

The project buried the old elevated Central Artery that used to slice through Boston, replacing it with a series of tunnels.

The most expensive highway project in U.S. history, the Big Dig has been plagued by leaks, falling debris, cost overruns and delays. The project was supposed to take seven years and $2.6 billion; it took nearly 15 years and $14.6 billion before it was all but completed earlier this year.

For months, amid complaints of delays, cost overruns, shoddy workmanship and inferior materials, Amorello had repeatedly assured drivers that the highway tunnels were safe.

But the fatal accident raised concerns about the safety of the tunnels — and investigations and criminal probes that are under way have zeroed in on the system of bolts-and-epoxy that have been used to hold up the ceiling panels, some of them weighing as much as 3 tons.

Almost immediately after the accident, Romney called on Amorello to resign. The governor also seized authority to oversee the inspections and to determine when portions of the tunnels, closed since the accident because of concerns about the bolt system, can reopen.

Even some of Amorello's staunchest supporters were soon suggesting he had become a distraction and should consider stepping aside.

"He is secretive and resists oversight by his own board, and refuses to share information," Romney said. "People should not have to drive through the Turnpike tunnels with their fingers crossed."

But Amorello had resisted those calls, saying it was important to get to the bottom of how the ceiling panels came down.

"All of our energies are to ensure that nothing like that ever happens again," he said. "It's a commitment I made to the family. It's a commitment I made to the people of Massachusetts."

Romney pressed ahead with his efforts to strip Amorello of his job as chairman and chief executive of the Turnpike Authority. Amorello sued to block a hearing Romney had scheduled for Thursday where he would serve as judge and jury to determine if there were justification to remove Amorello from his post.

John Moscardelli, a member of the Turnpike board since 2002, said he believes Amorello was wrongly blamed for construction problems that happened before he took over as chairman.

"I feel very, very badly for him. I know how hard he worked," Moscardelli said.

Moscardelli said Amorello told him he agonized over the decision to resign.

"He just felt that it was the right thing to do for the public, for the Turnpike Authority, and of course, for him and his family," Moscardelli said.

Jeffrey Denner, who represents Del Valle's husband, Angel, in a wrongful death lawsuit he plans to file, called Amorello "a very decent man in a very difficult situation."

"I think he had little choice (but to resign) given the fact that with all the damaging disclosures that have been made over the past week or so, it all happened on his watch, and I think he has to take responsibility for it," Denner said.