A key Spartanburg County roadway will soon boast South Carolina’s third “diverging diamond” interchange.
The project at Interstate 85 and SC Highway 290 in Duncan is about a year behind schedule, but construction is expected to finish before summer.
The innovation in traffic engineering is designed to move vehicles more quickly and safely through busy intersections.
Specifically, vehicles exiting I-85 and turning left onto Highway 290 won’t have to cross through an intersection. They will stay on the left side of the highway – keeping the traffic moving – before transitioning back to the right after crossing the bridge over the interstate.
“A lot of people find it a little scary and weird their first time through one of these interchanges, but after that they get used to it,” said Hannah Robinson, media relations manager with the South Carolina Department of Transportation.
Robinson said signs will be on prominent display to provide easy direction.
The state’s other two diverging diamond interchanges are in Fort Mill and the Chapin area, Robinson said. There is also an intersection featuring the design off of Interstate 26, at Airport Road, south of Asheville, N.C.
Construction has been held up by bad weather – especially Tropical Storm Helene and its aftermath – as well as supply chain challenges and design adjustments needed for utilities, Robinson said.
For now, construction means traffic is moving slowly through interchange, especially at peak times of day.
Arturo Marte said he drives through the area for work at about 4 a.m., so things aren’t bad during his morning commute. But it’s more hectic in the afternoon.
“It’s been like this for a long time,” Marte said, as he pumped gas at a QT gas station. “Hopefully, it will be finished soon, so the traffic will flow a lot better.”
Deborah Otto lives in Chesnee but travels to the Duncan area often. “I try to avoid coming this way,” she said. “It feels dangerous.”
Indeed, there has been an uptick in traffic accidents in and around the construction zone, said Duncan town administrator Cameron Fant.
“It’s probably every other day. Some are minor, but we’ve had one or two major accidents,” he said. “Our first responders spend a lot of time at that intersection.”
Fant said some frustrated motorists “call us and unload on us. We say, ‘This is DOT project.’ But we tell them the end result will be worth the frustration.”
The Duncan area is rapidly growing, and the old interchange needed an upgrade, Fant said. “Things will be much better once it’s all said and done.”
In addition to the new traffic pattern, the $17.9 million project also includes new lanes on each entrance ramp, as well as an extra westbound lane on Highway 290, Robinson said.
The existing 268-foot-long bridge is also being widened to accommodate a new pedestrian path along the center of the bridge.
A South Carolina Department of Transportation video shows how a diverging diamond intersection works.