BOSTON - When the clock runs out on 2007, Boston will quietly mark the end of one of the most tumultuous eras in the city's history: The Big Dig, the nation's most complex and costliest highway project, will officially come to an end.

Don't expect any champagne toasts.

After a history marked by engineering triumphs, tunnel leaks, epic traffic jams, last year's death of a motorist crushed by falling concrete panels and a price tag that soared from $2.6 billion to a staggering $14.8 billion, there's little appetite for celebration.

Civil and criminal cases stemming from the July 2006 tunnel ceiling collapse continue, though on Monday the family of Milena Del Valle announced a $6 million settlement with Powers Fasteners, the company that manufactured the epoxy blamed by investigators for the accident. Lawsuits are pending against other Big Dig contractors, and Powers Fasteners still faces a manslaughter indictment.

Officially, Dec. 31 marks the end of the joint venture that teamed megaproject contractor Bechtel/Parsons Brinckerhoff with the Massachusetts Turnpike Authority to build the dizzying array of underground highways, bridges, ramps and a new tunnel under Boston Harbor - all while the city remained open for business.

Some didn't know if they'd live to see it end.

Enza Merola had a front row seat on the Big Dig from the front window of her pastry shop - stacked neatly with tiramisu, sfogliatelle and Italian cookies - in Boston's North End.

During the toughest days of the project, the facade of Marie's Pastry Shop, named after her sister, was obscured from view. The only way customers could find the front door was along a treacherous path through heavy construction.

"For a while we thought we weren't going to make it," Merola said. "But you know, we hung in there."

The Central Artery/Third Harbor Tunnel Project - as the Big Dig is officially known - has its roots in the construction of the hulking 1950's era elevated Central Artery that cut a swath through the center of Boston, lopping off the waterfront from downtown and casting a shadow over some of the city's oldest neighborhoods.

Almost as soon as the ribbon was cut on the elevated highway in 1959, many were already wishing it away.

One was Frederick Salvucci, a city kid for whom the demolition of the old Central Artery became a lifelong quest.

"It was always a beautiful city, but it had this ugly scar through it," said Salvucci, state transportation secretary during the project's planning stages.

Rather than build a new elevated highway, Salvucci and others pushed a far more radical solution - burying it.

Easier said than done.

Those who built the Big Dig would have to undertake the massive highway project in the cramped confines of Boston's narrow, winding streets, some dating to pre-Colonial days.

Of all the project's Rubik's Cube-like engineering challenges, none was more daunting than the first - how to build a wider tunnel directly underneath a narrower existing elevated highway while preventing the overhead highway from collapsing.

To solve the problem, engineers created horizontal braces as wide as the new tunnel, then cut away the elevated highway's original metal struts and gently lowered them onto the braces - even as cars crawled along overhead, their drivers oblivious to the work below. *