Recognizing the need to minimize right-of-way impacts while efficiently handling the anticipated high traffic volumes, the City of Franklin engaged GS&P to develop a distinct and effective design that conserves valuable commercial property. The engineering design team, headed by principal-in-charge Michael Flatt, P.E., recommended a Single-Point Urban Interchange (SPUI) design. This design allows for increased traffic capacity and reduced delays by eliminating a step in maneuvering through the freeway interchange.
In the SPUI design, all traffic movements are initiated at one large intersection controlled by one traffic signal. When the traffic signal turns green, opposing traffic moves quickly through the intersection. This is more efficient than traditional diamond interchange design which contains signals at the end of both exit ramps causing left-turning vehicles to often wait at two traffic signals.
Though creating an intersection where all traffic movements are aligned to intersect at a single point is complicated, the elevated structure required for McEwen created an even greater deal of geometric complexity. Each freeway exit and entry ramp approaches and crosses the bridge with curved alignments. The bridge was designed to accommodate these ramp curves and traffic alignments, which required a wide bridge at each end that narrowed in the middle.
In order to incorporate unique aesthetics into the project, GS&P used the extra width of the bridge created by the ramp curves to design sidewalk plazas that include landscape planters, colored and stamped concrete, decorative metal pedestrian railings and 19th century-style lighting fixtures. The retaining walls were designed with exposed wall finishes and capstones to closely resemble the native fieldstone rock walls common to the area. These design elements, along with the welcome monument signs at the ramp islands, help create a sense of place and arrival.
The new freeway interchange has already significantly improved traffic conditions in the vicinity. On completion of the Carothers Parkway extension, which will intersect McEwen Drive, a significant number of Nashville commuters are expected to access Interstate 65 via the new interchange. And the aesthetic enhancements, not typically found in interchange improvement projects, have generated reactions of both surprise and delight among members of the community.