One of the most heavily traveled thoroughfares in the world is New York City's Avenue of the Americas (known to natives simply as "Sixth Avenue"). So when the city decided to rebuild the avenue in the early 1990s, it was taking on a worldclass challenge.

To make the job especially challenging, the city Department of Transportation determined that all the below-ground infrastructure and utilities would be upgraded before the roadway was fixed.

The project, begun in May 1990, was completed in October 1994, and "basically reflects a new way of looking at street reconstruction," says Evans Doleyres, the DOT'S director of roadway construction. "Ideally, one would like to look at all the underground structures and see if there's a need to rehabilitate sewers, water mains, etc., and do a thorough job so we don't have to go back in the near future."

A total of 115,000 square yards of roadway were reconstructed, half as composite pavement and half as full-depth reinforced concrete, with more than four miles of new curbing including 15,000 linear feet of new granite curb.

New traffic signals, street lights and fire alarm equipment were also installed, as were some three and-one-half miles of 12-inch diameter water-supply lines, two miles of 20-inch-diameter pipe and 200 feet of 36-inch steel pipe.

Nearly a mile of sewer was relined or replaced. And all had to be done in a space crowded with underground steam, gas, electric, phone and cable TV lines and two rapid-transit lines: the NYC Transit Authority's Sixth Avenue subway line and the Port Authority Trans-Hudson (PATH) commuter rail line.

Half the street was paved at a time, in six- to seven-block segments that were reopened to traffic in three days. (The 12-foot-wide curb lane was finished first, followed by the two inner lanes together.

At intersections, super high-early-strength concrete, which can be opened to traffic only six hours after pouring, was used. At the most heavily travelled intersections, work was confined to weekends only.

Special materials were used where the avenue passed through historic/landmark areas: Greenwich Village, the "Ladies' Mile" district of huge, cast-iron pre-world War I department stores and Rockefeller Center. A five-foot strip of bluestone was installed along the curb in Greenwich Village, and the remaining sidewalk was pigmented to match. The Ladies' Mile received similar treatment, and special 19th Century-style "Bishop's Crook" lampposts were installed in both historic districts.

Altogether, more than 20 different "special" sidewalks were installed, some of them using stone imported from Italy.

When problems arose, it was usually because records and maps of the under, ground infrastructure ranged from incomplete to misleading or nonexistent,-- no surprise in a city that has been continuously rebuilding itself for three centuries. Most of the project's delays -- it ultimately ran two years over schedule -- resulted from unforeseen field conditions.

Excavations exposed turn-of-the-century trolley yokes that had to be removed (the old track supports were just below the surface) as well as the footings for the long-vanished Sixth Avenue Elevated Railroad, built during the 1870s. Failing water mains were a recurring problem, while in another case a planned major water main relocation had to be abandoned: there was no space left to put in the new line.

Throughout the project, the DOT took great pains to establish and maintain good relationships with community and business groups and to alert the public to any changes that might affect them.

At one point, for instance, water service had to be briefly interrupted in an area that is home to Manhattan's wholesale flower district, but with advance warning, shop owners were able to take steps to protect their goods.

In addition, no businesses had to close down while work was under way, and the four-year project received an outstanding, zero-fatality safety record. New York City-based Gandhi Engineering provided construction inspection for the project.