Success Story: Missouri
Missouri Replaces Bridge on I-70

The voided slab bridge over I70 between Lake St. Louis Boulevard and Route 40/61 in St. Charles County, MO, was more than 40 years old, and traffic studies indicated the need for additional lanes to accommodate increased traffic. Through a value-engineering proposal, Missouri DOT's contractor suggested building a new, wider structure rather than widening the existing Lake St. Louis Bridge.

The contractor estimated that a new bridge could be built rapidly using precast deck beam sections and mechanically stabilized earth wall abutments, which would provide a two-span bridge instead of the existing four-span. Lane capacity would increase from two to six lanes, providing two through lanes and one turning lane in each direction. The cost would be an additional $500,000, but the new bridge would offer a safer clearance of 5 meters (16.5 feet) for interstate traffic, in lieu of the 4.9-meter (16-foot) clearance originally designed. In addition, the new deck beam structure would not restrict overheight loads. Finally, building the new bridge reduced the actual construction time and impact on motorists by several months.

The bridge closed on August 3, 2003, and reopened by November 24. The combination of the type of bridge (prestressed box beam) and closing the overpass during construction enabled the contractor to demolish the old bridge and erect the new one in less than 4 months. "To decrease the construction time, local officials agreed to allow the department to close the old bridge, demolish it, and build the new one," says Barry Bergman, project manager with the Missouri DOT.

By reducing the number of spans, the department improved the overall geometrics and increased the efficiency and safety of the interchange. The two-span bridge also allows for widening Interstate 70 to address capacity needs in the future. Maintenance costs decreased as well, since the new bridge was approximately 30.5 meters (100 feet) less than the original facility. An additional benefit of the new structure is that the bridge provides simple architectural enhancement opportunities (such as texturing and staining) for the city of Lake St. Louis.

The Missouri DOT built the new Lake St. Louis Bridge over Interstate 70 in St. Charles County, MO, as a safer, more cost-effective alternative to widening the existing bridge.