The section of the Lakefront Trail in Chicago between Navy Pier and the Chicago River is one of the most heavily used portions and required structural and way-finding changes to better accommodate users.
The proposed flyover had to stretch from the Ohio Street Beach on the north side of the Chicago River to DuSable Harbor on the south, with a spur ramp to Navy Pier. Users would see the structure from both above and below, so the Chicago DOT wanted a solution that blended engineering and architecture into a piece of multimodal public art.
HNTB developed the concept of an easily manipulated central steel spine and a longitudinal spine-rib support system that allows the bridge to curve up, down, and around as needed, which also provides an exciting and dynamic visual impact that gives a feeling of a roller coaster.
At one point the flyover squeezes between Lake Shore Drive and a 70-floor condominium tower in a series of horizontal and vertical curves, requiring “delicate surgery” to be performed on that stretch of the Drive. Another challenge was the point at which the flyover splits into a “Y,” with one path descending slightly upward then down again to Navy Pier, and the other beginning an upward, twisting path between upper Lake Shore Drive and the condominium building before descending to ground level at the northernmost point. The supporting columns are topped with a saddle-like configuration that would suggest human hands holding up the pipe while transitioning the load downward. Specially designed lugs link expansion joints to provide torsional continuity and allow for temperature driven expansion and contraction.
The flyover weaves its way up into the air and then down again as it spans the Chicago River and heavy traffic below. It has been described as looking like “the spine of a giant dinosaur,” an airplane taking off and soaring into flight, or even a roller coaster. The solution is less treacherous and allows users to traverse the trail faster.