Tri-State's new Mile Long Bridge will rise alongside original structures
How do you tear down an iconic bridge carrying 150,000 vehicles a day and construct a replacement without causing a traffic meltdown of cataclysmic proportions?
Build the new structure next to it.
Starting this month, the Illinois tollway begins work on the northbound section of the Tri-State Tollway's Mile Long Bridge near Willow Springs.
It's not apparent when you're driving on it, but the "bridge" is actually two side-by-side structures.
Crews will start building a new northbound bridge next to the existing one that will increase from four to five lanes to alleviate congestion. The shoulder lanes also will be widened to accommodate Pace express buses at a later date, planners hope.
"The existing structure's been out there since 1958," said Chief Engineer Paul Kovacs, who described the existing bridge deck as a "hodgepodge" of overlays, repairs and new pavement.
Construction shouldn't affect drivers except where the replacement ties into the existing toll road at both ends. That should result in some minor traffic shifts and temporary lane closures at off-peak times.
The northbound bridge will cost about $184.6 million; the entire project including demolition and construction is estimated to cost up to $450 million. It's part of a massive $4 billion widening of the Central Tri-State (I-294) between Rosemont and Oak Lawn.
When the first structure is completed in 2020, northbound traffic will be shifted to it. Then the old bridge will be demolished, and a southbound one put up in its place. Southbound vehicles will be moved over when the second new bridge is finished in 2023.
"The last step will be to take out the old southbound bridge," Kovacs said. The rotation "should have a lot less impact on the motoring public."
The Mile Long Bridge offers unique challenges spanning the Canadian National and BNSF railways, a UPS distribution center, 75th Street, the Des Plaines River, Illinois and Michigan Canal, and Chicago Sanitary and Ship Canal.
It's like "we're spanning a whole city," Kovacs said.
Adding to the complexities are underground gas lines and a jet fuel line to O'Hare International Airport.
The new bridges will have longer sections, or spans, and be supported by fewer piers, the sturdy columns that support the structure. That means fewer bridge joints, which are usually the first to require repairs, Kovacs said.
How long will the new bridge be? About 4,800 feet, similar to the original, and 480 feet short of a mile.
"The deck of the new Mile Long Bridge at its highest point is projected to be 54 feet above the ground. That's a few feet higher than the existing bridge," spokesman Dan Rozek said.