New I-70 Mississippi River Bridge

Relocating part of a busy interstate that links Illinois to St. Louis was just one of the many challenges faced by the Illinois and Missouri Departments of Transportation. Their goal was to select a bridge type, with the winning structure being a river spanning cable-stayed bridge. Modjeski and Masters was selected for both the bridge studies and preliminary and final bridge designs. The task included an 18-month bridge type selection study, with the winning structure being a river-spanning cable-stayed bridge. 

The I-70 Mississippi River Bridge would be no ordinary structure. With a width of 222 feet, it would be the widest cable-stayed bridge in the world. Four traffic lanes, plus two full shoulders in each direction, would carry the relocated Interstate 70 and Interstate 64. Our design called for several innovative features: two single-pylon towers, inclined nine degrees from the river, which would eliminate obstructions to river traffic; a main channel span of 2,000 feet; and three planes of cables. To eliminate the potential threat of a vessel impacting the vital structure, and at the same time satisfy the demand for a massive and recognizable landmark, the winning cable-stayed bridge would span the entire width of the Mississippi River with no piers in the water. Equally important was the extensive site-specific seismic analysis of the bridge, which sits within the New Madrid Seismic Zone. The resulting solution featured several internal design mechanisms to help minimize and redistribute stresses caused by a seismic event.