City Hopes $6.4 Billion Will Erase Ugly Scar : A hated elevated road jams traffic, cuts downtown from the waterfront. By 2002 it should be gone.

It’s part of the fabric of life in Boston, no less so than the city’s well-marked walking trail of historic Colonial sites. But unlike that tourist attraction, the Central Artery is the source of little pride--and much aggravation.

The artery is a stretch of Interstate 93--most of it elevated--that links the northern and southern ends of Boston. Built in the 1950s and designed to accommodate fewer than half of the 190,000 vehicles that now travel it daily, it has long been called an example of transportation planning at its worst.

Jammed in both directions for eight to nine hours a day, the Central Artery is the source of frayed nerves and unhealthy air. The elevated portion, with its rusting green supports, has long been seen as a scar on the city’s landscape and a barrier between its waterfront and downtown.

But after decades of planning, the state is moving ahead with a plan to correct the artery’s problems and to meet another longtime goal: to provide a direct interstate highway connection to Logan International Airport in East Boston.

The 10-year, $6.4-billion venture--being carried out with 86% federal funding--involves replacing the elevated roadway with a mostly underground road eight to 10 lanes wide and building a four-lane Boston Harbor tunnel to link the Massachusetts Turnpike to the airport.

When it is completed early next century, the artery’s capacity will more than double to 225,000 cars a day, while removing the hated elevated road.

The new tunnel, which will follow a route far south of the existing Sumner and Callahan tunnels under the harbor, will divert airport-bound traffic from the artery.

The huge project will also add a commercial access road to the waterfront, create a utility corridor and give the city 200 acres of open space.

Most important, many say, it will re-link Boston’s waterfront and downtown.

City officials say they hope that the artery project, nicknamed the “Big Dig,” will help revitalize a region that has fallen on hard times.

Peter M. Zuk, project manager for the Massachusetts Highway Department, said the new roadway and tunnel, combined with improvements to the mass transit system that will accompany the project, will give Boston the “most sophisticated highway infrastructure” of any city.

State Transportation Secretary James J. Kerasiotes said the project “is going to leave behind a spectacular urban product for our children and grandchildren--a much more livable, exciting, attractive Boston,” that will stimulate economic growth.

Members of Boston’s business community tend to agree. William Coughlin, president of the Greater Boston Chamber of Commerce said the “knitting of the waterfront to the city will be an incredible urban design enhancement.”

But not everyone is so enthusiastic.

Andreas Aeppli, a mass transit advocate, said the Big Dig could be called “a grandiose waste of money” whose support is “a mile wide and an inch deep.”

The project drew heated opposition from a diverse range of environmental and community groups, but an accord last year largely cooled those passions.

Under the agreement, officials consented to include major extensions of commuter rail and subway lines in the project, as well as add bus and car-pool lanes and provide better parking management. In return, a coalition of groups agreed to suspend a lawsuit they had filed.

Steven H. Burrington, attorney for the Conservation Law Foundation, which had initiated the lawsuit, said that if the state lives up to its promises, his group could support the project because it is being “undertaken with the recognition that highway expansion itself is not a solution.”

At least one thorny issue remains to be settled, however.

After protests from environmental and neighborhood groups, the state agreed to reconsider a proposed elevated interchange over the Charles River. Opponents said it would be an eyesore, and officials have yet to announce a final design.

Such design changes have set the project’s timetable back two to four years, Zuk said. Completion is now slated for 2002 or even later. Cost estimates have risen from the original $3.3 billion to $6.4 billion.

Officials said their largest challenge is minimizing traffic disruption during construction.

Traffic problems will increase as crews begin digging a tunnel for the artery early next year. Though the elevated highway will remain in place during the work, “we’re not going to be able to solve every problem in advance,” Kerasiotes said.

Officials says they believe that any disruption will be outweighed by the project’s lasting benefits. Noting that the present nine-hour traffic jams on the artery would swell to 14-hour jams by the year 2010 if nothing were done, Zuk said: “That’s an unacceptable condition from a transportation standpoint, an economic standpoint, and . . . an environmental standpoint.”