The intersection of US 78/SR 10 and SR 124 sits at the heart of Snellville and south Gwinnett County in Georgia. After experiencing years of worsening traffic conditions at this pivotal intersection, the Georgia Department of Transportation (GDOT) approached Gresham Smith to develop a cost-effective conceptual design solution that would ease the extreme congestion while minimizing impacts to adjacent properties.
Following the evaluation of several concepts for a preferred alternative, we identified an innovative two-legged continuous displaced left-turn (DLT) intersection—also known as a continuous flow intersection (CFI)—as the most viable solution. Our final DLT design not only successfully addressed both traffic and local community concerns, but did so under budget and within a shorter construction time frame as compared to other alternatives considered.
DLT in Georgia
and only single-span, arch truss signal bridge in the state
community members attended educational public information open house
Reconfiguring Left TurnsOur solution redirects traffic onto an underutilized bypass while managing the heavier volumes through the DLT intersection. The design allows US 78/SR 10 left-turning and through-traffic to move simultaneously, increasing efficiency and improving safety by reducing potential conflict points. Traffic signals at the left-turn crossovers and the main intersection are operated in a coordinated mode so that vehicles don’t stop multiple times in the intersection area.
Setting a PrecedentThe project is only the second two-legged DLT to be constructed in the state of Georgia. When Gresham Smith began designing the intersection in 2007, there were no precedents for the design of this type of project. This challenged our engineers with implementing the design in a context-sensitive manner. Opened to the public in 2019 with minimal impacts to surrounding land uses, the DLT serves as a case study for future projects of its type, demonstrating how it improves safety, mobility and traffic congestion through unopposed left turns and simpler traffic signal phases.
Evoking Community PrideThe intersection also included the installation of the first and only signal truss bridge in Georgia, which is comprised of a 191-foot-long, single-span arch truss. Because the intersection is located in the heart of downtown Snellville, the bridge not only had to function efficiently for traffic operations, but also had to serve as an iconic gateway to the city. The end product is an aesthetically pleasing, cost-effective marquee structure that effectively accommodates signal infrastructure while defining a brand for the city of Snellville that evokes a sense of pride in its residents.
Listening & LearningOne of the most significant achievements of the project was securing vital buy-in from the community. As previously proposed alternatives would have yielded major impacts to properties, including the closure of several businesses and infringement on historic landmarks, the project had already incurred significant opposition by the time GDOT and Gresham Smith began working on the revised concept.
As part of the Citizen’s Advisory Committee process led by our team, we listened to the concerns of a representative group of stakeholders and then demonstrated how a DLT would improve mobility with far less impact on properties. Once buy-in was gained from this group during a Public Information Open House (PIOH), they served as advocates for the project, educating other members of the public about the benefits of the DLT.
A Solution Worth Rallying AroundPrior to the DLT intersection, the major traffic delays occurring through this section of downtown Snellville were impacting economic development. The DLT alternative maintained the all-important core of the city center, providing citizens, elected officials and business owners alike with a design solution they could all rally around. Enhancing the safety and flow of all modes of travel, our DLT design is responsible to Snellville’s residential and business communities, while preserving the area’s key historic, social and natural environments.
Giving the Public a Bird’s-Eye View
At an Educational PIOH planned and facilitated by Gresham Smith, we educated motorists on how to navigate the new DLT. Our team worked with GDOT to develop numerous educational materials in a short time frame, including displays on the new lane configurations, traffic signals, vehicle movements and turn prohibitions. We also worked closely with GDOT’s Visual Engineering Resource Group (VERG) to develop a four-minute video with a bird’s-eye-view traffic simulation demonstrating how to navigate the new intersection and adjacent bypass. Over 200 members of the public attended the Educational PIOH.