Snaking through the heart of downtown, Wacker Drive presented rebuilders with one of the most challenging transportation projects ever undertaken in Chicago.

Wacker abuts no fewer than 18 high-rises and a dozen parking facilities, requiring builders to orchestrate complex staging to keep 60,000 vehicles and 150,000 pedestrians moving while completely rebuilding a major section of the thoroughfare. Work on the adjacent Congress Parkway Interchange required similar consideration to accommodate 76,000 vehicles.

Every stage required creative solutions and extensive advance notice through new and traditional media. To minimize disruptions, workers revised staging on evenings and weekends, monitoring new patterns for problems and, when warranted, revising them.

The project marked the second and final phase of a program begun in 2001, when Chicago's Dept. of Transportation (CDOT) rebuilt an east-west section of the double-decker viaduct. Phase 2 focused on a north-south section.

The project was precipitated in part by extensive cracking and crumbling around upper-deck expansion joints, the result of thermal cycling and salt exposure over decades of service.

Today, the newly reconstructed deck rests on deep ribs and column-mounted bearings and is post-tensioned in two directions, accommodating loads imposed by new median planters.

Efforts required 15 post-tensioned bridge deck pours, some involving up to 1,700 cu yd of high-performance concrete. In addition to testing and placement of duct strands and reinforcing steel, pre-pour meetings and expedited requests for information addressed grouting, post-tensioning and closure pours. Some routed as many as 100 concrete trucks within allotted time frames during rush hour.

Early in planning, CDOT identified potential delays to the $300-million project. More than a year before contracts were awarded, utilities began relocating facilities that would have conflicted with the new foundations.

Wacker Drive Viaduct and Congress Parkway Interchange Reconstruction, Chicago

Key Players

Owner City of Chicago Dept. of Transportation

GC Transystems Corp., Chicago

Designer Alfred Benesch & Co., Chicago; T.Y. Lin International Group, San Francisco