‘Diverging diamond’ coming to I-40 interchange south of Raleigh. What drivers should know

Drivers will soon encounter a new traffic pattern at the Jones Sausage Road interchange with Interstate 40, one that has them briefly driving on what would normally be the wrong side of the road.

Next week, contractors for the N.C. Department of Transportation will begin converting the interchange into a diverging diamond. They hope to finish the work by October, making Jones Sausage Road the second diverging diamond interchange, or DDI, in the Triangle.

Two others are under construction, at I-40 and N.C. 42 in Johnston County and on I-40 at Airport Boulevard near Raleigh-Durham International Airport. A fifth is planned at the I-440 Beltline interchange with Wake Forest Road and two more are included in NCDOT’s plans to turn Capital Boulevard into a freeway between Raleigh and Wake Forest.

Diverging diamonds are still new to most Triangle drivers. The design involves crisscrossing traffic at either end of the interchange in a way that eliminates left turns across traffic and the amount of time drivers spend sitting at red lights.

That means drivers will find themselves briefly on the left side of the road as it passes under or over the highway. While the concept sounds daunting and may look it on paper, traffic engineers say the movement is intuitive and drivers quickly get the hang of it.

The new Jones Sausage interchange is part of a larger effort to widen I-40 from Raleigh south into Johnston County, which got underway in 2018. When plans for the project were presented to the public in 2017, NCDOT anticipated the interchange would remain essentially as it is today.

But then Amazon announced that it would build a distribution center on the Garner side of the interchange, with thousands of employees and hundreds of trucks coming and going each day. NCDOT and the town agreed that the existing configuration of the interchange would be overwhelmed, said NCDOT spokesman Aaron Moody.

“It’s going to have to handle more traffic,” Moody said. “And we know the DDI does that safer and more efficiently.”

The elimination of left turns across traffic will make it easier for trucks in particular to get on and off the highway, Moody said.

Another advantage: DDI’s handle more traffic without taking up more real estate. Contractors will be able to create the DDI pattern at Jones Sausage without building a new bridge, Moody said. Next weekend, workers are scheduled to rehab the deck of the existing bridge before starting on the new traffic pattern.

Diverging diamond interchanges planned

At least six other diverging diamond interchanges are in the works in the Triangle. Here’s the status of each one:

▪ Western Boulevard: Drivers began using the new DDI pattern here in November 2021, but the interchange isn’t finished. Contractors need to do extensive drainage work where Western passes under the Beltline and install permanent barriers and lane markings. The interchange will be finished sometime next year, along with the rest of the Beltline widening project.

▪ N.C. 42: The diverging diamond is part of a more extensive overhaul of the I-40 interchange in Johnston County’s Cleveland community, which will include new ramps that give drivers the option of getting on or off at nearby Cleveland Road. It’s scheduled to be finished next year.

▪ Airport Boulevard: Contractors will soon begin laying girders for a second span over I-40 and rebuilding one exit and one entrance ramp. But the diverging diamond pattern likely won’t be in place until sometime next summer.

▪ Wake Forest Road: NCDOT presented plans in 2018 for a DDI where Wake Forest passes under the Beltline. The project has been delayed, but the state expects to award a contract in the spring of 2026, with construction due to begin later that year.

▪ Durant and Perry Creek roads: NCDOT’s plans to convert Capital Boulevard into a freeway north of I-540 include turning the intersection of Durant and Perry Creek roads into a DDI interchange. The state plans to begin construction in late 2025.

▪ Falls of Neuse Road/South Main Street: The Capital Boulevard freeway plans also include a new DDI interchange at Falls of Neuse Road and South Main Street in Wake Forest. But NCDOT doesn’t yet have the money to build this section of the freeway and likely won’t get started until at least 2035.