The City of Alcoa, Tennessee, was facing an increase in traffic congestion at the US 129/Bessemer Street interchange, compounded by the addition of a large commercial development and a road widening project filtering more traffic into the interchange. Restricted by a limited construction budget, Alcoa sought the expertise of Gresham Smith to develop a cost-effective solution.
After considering several alternatives, including traditional solutions such as widening the road and reconstructing the intersection’s bridge, Gresham Smith’s engineers proposed a Diverging Diamond Interchange (DDI) design. No such interchange existed in the southeastern United States at the time, but the unique configuration improved traffic capacity, minimized cost and eliminated the need for drastic reconstruction. The City was further encouraged by the design’s anticipated impact on safety and the shortened construction schedule, and ultimately selected the DDI configuration after multiple public meetings and reviews of the proposed traffic flow.
Since opening, the City has not experienced any backup at the intersection, even at rush hour, and the DDI addition has contributed to traffic reductions at adjacent intersections. Accident rates have also decreased, with no incidents attributed to the design since the DDI opened.