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CHARLOTTE, N.C. ─ The engineers at STV/Ralph Whitehead Associates have developed an innovative interchange design in concert with their build-partner, The Lane Construction Corp., that will help complete the heavily traveled Outer Loop of Charlotte.

For the recently awarded $93 million Interstate 85/485 interchange design-build contract, STV/RWA chose to explore an alternative design during the technical proposal phase. The "turbine interchange" was the alternative that was selected and is expected to provide significant cost savings during construction. Once completed, it will be the first interchange of its kind in North Carolina and one of just a small handful of similar designs in the entire United States.

The original plan for the interchange called for a modified clover, which was then redesigned to a four-level stack design to eliminate low-speed loops. The redesign was problematic because it included a number of high-level, long-span bridges that would be difficult to construct, and it would require an off-site detour for interstate traffic. Within that same footprint, the turbine interchange design created by STV and Lane Construction offers a two-level configuration with semi-directional ramps and utilizes smaller, single-span bridges, smaller columns, and flatter roadway profiles. The turbine design also will have less impact on traffic during construction and make it easier to widen the roadway in the future. The turbine interchange uses less construction materials, which will shave about $30 million from the original project costs while providing a safer and efficient interchange for motorists.

Construction on the interchange is expected to begin next year and is scheduled to be completed in 2014. Once finished, the project will fully close Charlotte's Outer Loop, I-485, which connects to major roadways such as I-77, NC 16, NC 115, and US 74. An analysis by the North Carolina Department of Transportation projects that the Outer Loop will carry about 130,000 vehicles per day by 2035.