CDM Smith teamed with Blythe Construction and the North Carolina Department of Transportation (NCDOT) to complete the I-485 Charlotte Outer Loop using design-build-finance delivery, the state's first use of alternative financing. Design-build-finance delivery, coupled with innovative interchange designs sped up project delivery and reduced overall project costs while improving safety and traffic efficiency. Sections of the I-485 outer loop had been opened to the east, south and west of Charlotte, though funding shortages left the northern portion incomplete. Closing the northern portion of this important corridor for local and regional traffic was deemed a top priority by NCDOT. Construction of the $140 million project was completed in June 2015.
Several innovative design features were used to help drivers enter and exit the new roadway quickly and safely.
The new, 5.7-mile eight-lane divided interstate completes the 67-mile I-485 Charlotte Outer Loop, closing the final segment from west of NC 115 to west of I-85. Completion of this final section of I-485 provides a high-speed freeway connection between I-77 and I-85, and relieves congestion on neighboring streets. Within the 5.7-mile northern section, several commercial and environmental obstacles were traversed, including Norfolk Southern Railroad and the Stony Creek tributary.
Innovative interchanges were included to help drivers enter and exit the new freeway quickly and safely. A split diamond interchange was constructed in a mixed-use development area to provide traffic in each direction an exit onto a one-way service road parallel to the freeway. Connectivity between these parallel service roads was provided by a series of three bridges crossing I-485 with roundabouts at both ends of each bridge. Additionally, one of the first diverging diamond interchanges (DDI) on the east coast was included where Mallard Creek Road crosses I-485. A DDI requires the two directions of traffic to cross to the opposite side while crossing a bridge over an interstate. This new design type—only recently introduced in the United States—provides many safety benefits, including fewer conflict points, better sight distance, reduced wrong-way ramp entry and increased room for trucks to maneuver.
In addition to roadway, interchange, bridge, retaining wall, culvert, sound barrier and signal designs, CDM Smith provided project management and quality control, location and right-of-way surveys, traffic capacity analysis, geotechnical and hydraulic engineering, and right-of-way acquisition services for the project.