Whoever said that life is too short to live by a schedule never tried to replace a bridge on one of the busiest thoroughfares in the nation.
Keeping to any schedule can be tough. But when it comes to replacing a key bridge on a heavily traveled American highway, even creating a suitable schedule can be challenging. Consider U.S. Rte. 1. Stretching more than 2,000 miles from Key West, Fla., to Fort Kent, Maine, the 83-year-old highway is both a landmark and an essential thoroughfare. Those dual roles are particularly evident along the stretch of U.S. 1 over the Millstone River near Princeton, N.J. A seemingly nondescript structure spanning a pastoral scene, the 111-ft Millstone River Bridge is an absolutely vital conduit for one of the most important roads in the nation.
Handling nearly 100,000 cars per day, this particular section of U.S. 1 is a major artery linking West Windsor Township in Mercer County with Plainsboro Township in Middlesex County. Viewed in a slightly larger context, U.S. Rte. 1 connects New York and Philadelphia—and every town in between. As for the Millstone River Bridge, it was originally built in 1928 and rehabilitated in 1959. Providing three traveling lanes in each direction (with no shoulders), the deteriorating three-span bridge had to be replaced. And that’s where the challenge began.
“Route 1 is a vital north-south regional corridor,” observed Project Manager John Campi Jr. of the New Jersey Department of Transportation (NJDOT). “Although the Millstone River Bridge must be replaced immediately, the closure of Rte. 1 is not an option. NJDOT met the challenge of designing a project to replace the bridge while maintaining six lanes of traffic.”
Pre-planning
Replacing any structure under live traffic is rarely easy. Add to that heavy traffic volume as well as a host of environmental issues, substantial utility concerns and the presence of a very well-protected bald eagle, and the challenge escalates by an order of magnitude. Here’s how.
Though the project presents some fairly traditional environmental constraints—freshwater stream restrictions and more common protected species mandates, for example—there also is a bald eagle nesting very close to the bridge. And the resulting protection requirements for the eagle intensify the scheduling challenge considerably. In fact, both calendar dates and the types of work possible at any given time are dictated by the effect they have on the eagle. In fact, many thought that creating an efficient schedule would be virtually impossible with the specified restrictions.
Using conventional methods and working within the given constraints, a project of this type would normally take three to four years to complete. But considering the state of the bridge, NJDOT wanted it done quicker. So when a conventional approach produced unacceptable projected timelines and considerable disruption, the experts got creative. Working closely with the New Jersey Department of Environmental Protection (DEP) and the utilities, and using some unconventional means and material, NJDOT and the project team found a solution.
“The primary goal of the project is to replace the original deteriorated structure with a two-span structure and widen the bridge. NJDOT will add three travel lanes to the bridge in each direction, with auxiliary lanes, shoulders and sidewalks,” explained AECOM Project Manager George Sholy. “But rather than take up to four years, NJDOT will expedite construction so as to finish in 24 months or earlier.
“To save time and advance the schedule, we’ve advocated the use of prefabricated superstructure units. We’ll have them delivered, and a crane will pick them up during night hours, placing the units right on the reconstructed piers and abutment walls. We’ve done this before on other bridges in New Jersey and it worked very well. We’re also going to use precast elements for retaining walls and potentially for the bridge parapets.” But even after condensing the schedule with prefabricated elements, the greatest constraint was most definitely environmental.
“Though there are fisheries in the river, as well as a long-eared owl and some Indiana bats that must be addressed, the real issue here is the bald eagle. Nesting very close to the site—we’re not allowed to reveal exactly where—the bald eagle will be very carefully monitored throughout the construction period. A DEP monitor will actually be present to observe the bird. Any time the bird appears to be disturbed, NJDOT will ask the contractor to address the noise or to modify the construction method so that it’s less intrusive. Since the bird already lives close to a busy highway, we don’t expect too many interruptions. However, we’re making sure that everyone understands the restrictions that eagle can represent.
“This approach might seem like a hardship to many contractors. But without that degree of sensitivity, construction would have had to shut down for nine months of the year. And working only three months of the year was unacceptable. So we worked out a compromise that protects the eagle and advances the project. But that was by no means the only challenge on the project.
“For example, each of the eight utility stakeholders imposed its own constraints on how and when those utilities could be handled. The electric company decreed that their utilities could not be interrupted or even ‘touched’ during their peak summer period. The gas company levied the same restriction, but in the winter. Every phase of the project must confront challenges of one form or another. So we’re threading the needle every day on this project. There is little room for error, but it is still a workable schedule.”
Camera ready
Though the bald eagle will have a captive audience at all times, it is by no means the only thing under observation. NJDOT will install cameras to observe traffic during construction. By having the live feed coming straight through to their offices, NJDOT staffers will be able to respond to traffic issues immediately. At the end of construction, the cameras will become a permanent feature of the bridge and roadway. But timesaving measures were not only applied to the construction schedule itself.
The project team also chose to use galvanized steel girders for the bridge because there is very little clearance between the bridge and the water, and the lack of clearance makes maintenance painting difficult and potentially dangerous. After examining many different coatings and methods, the project team determined that galvanized steel offered the best strategic solution. Galvanized steel provides substantial savings from an operations and maintenance perspective. NJDOT will never have to paint the bridge, saving both time and money.
The Millstone River Bridge is a key element of U.S. Rte. 1. Though the traveling public will have full access to every lane on Rte. 1 during construction, they also will soon benefit from a new, striking, durable bridge because of an accelerated construction schedule that addresses a range of challenges. With construction awarded in February 2009, the new Millstone River Bridge will be completed in December 2010—years ahead of the most optimistic original expectations.
Keeping any schedule can be tough. And when it comes to replacing the Millstone River Bridge on U.S. Rte. 1, just creating a schedule was challenging. But the New Jersey Department of Transportation has met that challenge. Whoever said that life is too short to live by a schedule never had to replace a bridge on one of the busiest thoroughfares in the nation.
