Bridge Description

Over I-70 in St. Charles County, about 3.4 miles east of Route 61

Tier 5 (within 3 months)

ABC: three months; Conventional: 6-9 months of construction with major interstate traffic impacts

reduced traffic impacts, improved work-zone safety, improved site constructability

134-ft long and 84-ft wide two-span (67 ft - 67 ft) adjacent box beam bridge

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Traffic management alternative, if constructed conventionally: extended detour

The existing two-lane, four-span (50 ft - 59 ft - 58 ft - 50 ft) continuous concrete voided slab bridge was 217-ft-long and 31-ft-wide. Built in 1964, it needed to be widened to reduce congestion.

The replacement bridge has four 12-ft-wide traffic lanes, two 10.67-ft-wide shoulders on each side, and a 12-ft-wide turn lane in the center. The cross-section consists of 21 four-ft-wide and 27-inch-deep pretensioned adjacent box beams with 5.5-inch-thick cast-in-place concrete composite deck.

MODOT accepted a contractor’s value-engineering proposal to rebuild the bridge using prefabrication instead of widening the existing structure. The new bridge used pretensioned adjacent box beams and MSE wall abutments with steel H-piles. The prefabrication allowed a design with two spans rather than the existing four spans.

Although costs increased, the contractor’s proposal offered both short- and long-term benefits. The new design had fewer spans, improving the geometrics of the interchange and increasing its safety and efficiency. Fewer spans also result in lower maintenance costs. By eliminating the need for formwork, which was required for widening the existing bridge in place but would have reduced clearance on IH70, the value-engineering proposal using prefabrication improved work zone safety by reducing the amount of time workers had to operate in low-clearance conditions. With prefabrication facilitating faster construction, bridge users were spared several months of inconvenience, and IH70 users were spared a period of reduced vertical clearance. Motorist safety increased because falsework towers were not needed in the outside shoulders. In addition, the new structure is more aesthetically appealing.