By Jessica Harper
Bridge Builder Magazine, April-May, 2003
Recycled Structures: Temporary bridges at Boston's Big Dig get reused
Boston's $14.6 billion Central Artery/Tunnel (CA/T) project, nicknamed the Big Dig, has initiated the largest bridge recycling program in the United States. With about 14 temporary structures used on the project in 13 years, the Massachusetts Turnpike Authority (MTA) announced in 2001 that it would reuse them across the state.
Considering the enormity of the Big Dig, the cost overruns and subsequent bitterness from other Massachusetts cities, and the state's bridge conditions (595 structurally deficient and 944 functionally obsolete at the time), the MTA knew it had a good idea, even though it hadn't planned it. The first time temporary structures were recycled at the Big Dig was more than 10 years earlier.
Near the beginning of the project, Charleston Mass. donated a secondhand modular through-truss bridge made by Baltimore-based Mabey Bridge and Shore. It was installed at vent #6 on the Ted Williams Tunnel.
One of the Big Dig's first major accomplishments, the tunnel carries traffic fron South Boston, beneath Boston Harbor, and to Logan Airport, where modern Continental, Cambridge Mass., had installed another temporary bridge around the same time. "The tunnel cuts through an important part of the airport, with several large transport companies located there," says Bill Killeen, President and owner of Acrow Corp. of America, Carlstadt, N.J. "The contractor had to maintain traffic to these places."
Acrow supplied the 150' x 34' structured that was installed over flat land so crews could start digging underneath it. The four-lane tunnel was completed in December 1995. Modern Continental returned the temporary bridge to the state transportation agency and later used it to maintain traffic at a sand and gravel plant on another Big Dig Contract.
As the project progressed, The MTA specified several more temporary bridges to alleviate traffic congestion and driver inconvenience during construction.
Maintaining Traffic
Boston houses almost 600,000 people. Maintaining traffic during construction is a top priority for owners, city officials, and, especially, drivers. "You have to take into account the cost of the drivers' time and fuel while they are trying to get through a construction site," Killen says. "It doesn't take very long for a temporary structure to pay for itself."
Acrow has sold three other bridges that are still on-site: one 130-foot span over the Massachusetts Turnpike: one 60-foot span serving as an exit/entrance ramp, and one 240-foot long, two span structure. The MTA purchased all three, which are designed for HS 25 loading, with a 10 year life span. They've been in place for about 6 years. Of the approximately 11 bridges on-site made by Mabey Bridge and Shore, Kevin Traynor, sales representative, says the state owns about 70 percent. Although mostly used in temporary situations to maintain traffic, Traynor adds these temporary bridges certainly can be reused - sometimes as more permanent crossings.
Mattew Amorello, MTA chairman, championed their reuse in other locations. Afterall, he was the commissioner for the Massachusetts Highway Department (MassHighway) and understood the state's needs firsthand. According to MTA spokesperson Sean O'Neill, "Amorello identified priority structurally deficient bridges throughout the state and saw a way to put these temporary structures in place, " he says. "It was an excellent fusion of two departments."
For state or city transportation agencies seeking a short-term solution without a long-term investment, several companies including Acrow and Mabey Bridge and Shore, will rent bridges.
For MTA and MassHighway, the best decision was not only to buy the bridges but also to reduce costs and reuse resources by recycling bridges.