Innovative Gantry System Improves Traffic Flow While Rebuilding Fox River Bridge
Rebuilding the Fox River Bridge in Elgin, Illinois, is one of the largest single awards in the $2.5 billion rebuilding and widening of the I-90 Jane Addams Memorial Tollway between the Tri-State Tollway (I-294) and Rockford. Originally opened in 1958, the six-lane bridge is being replaced with two side-by-side bridges, 1,315-feet long, standing 40 feet above the Fox River. The new structure will increase capacity to eight lanes with full shoulders in each direction. The bike and pedestrian bridge that runs under the structure are also being replaced. Stanley Consultants designed the $95 million Illinois Tollway project.
More than 100,000 vehicles travel across the Fox River Bridge each day. That equates to nearly 110 million vehicles traversing the bridge during the three-year construction period. Maintaining traffic flow while simultaneously demolishing the existing structure and building a new one is traditionally accomplished by developing a multi-staged plan that jockeys traffic back and forth across the bridge section with split counter-flow lanes and numerous sub-stages. However, by selecting girders that significantly increase the structural depth of the bridge, it became possible to construct the entire substructure of the new bridge underneath the existing bridge. This significantly lessens the impact to traffic by allowing construction of the new substructure under the existing bridge without interruption—even through the winter. This made it possible to reduce the maintenance of traffic scheme to just three stages.
A gantry system, used instead of conventional cranes to perform the heavy lifting, also improves traffic flow by allowing all six lanes to remain open during construction. The gantry uses a hoist traveling along an overhead rail to lift and set the heavy beams, each weighing nearly 100 tons. All pier elements, including pier caps, are being constructed under the bridge while maintaining all traffic lanes above, which allows the contractor to work unobstructed. These innovative engineering and construction techniques are expected to shorten the construction period and are also anticipated to save $2.2 million in maintenance costs over the life of the new bridge.