March 4. By Dave Vieser. The next time you become frustrated while sitting in congestion on the Exit 28 DDI overpass, keep this in mind: according to a 10-year report compiled by the Cornelius Police, the DDI has cut accidents at the intersection by nearly half when compared with pre-DDI accident levels.

Moreover, there have been no fatalities at Exit 28 attributed to the DDI—short for diverging diamond interchange—since it opened in 2014.

While the design came under fire when it was first proposed, police and transportation officials say they are not surprised by the report’s findings.

Cornelius Police Chief David R. Baucom

“The DDI has been a great improvement for drivers in Cornelius since it was installed more than 10 years ago,” said Cornelius Police Chief David Baucom. “Although our community has continued to grow and we still face traffic congestion, there is no doubt this project has been directly responsible for a decrease in accidents and improved safety overall.

State transportation officials concur.“The reductions Cornelius Police cited in their report are consistent with the statistics NCDOT sees at diverging diamond interchanges across the state” said spokeswoman Jen Goodwin. “When properly implemented, these designs save lives by reducing severe crashes and injuries.”

By the numbers

There has been a 44 percent reduction in total number of accidents: 45 in 2013—the year prior to construction of the DDI—compared to 25 in 2024

The number of angle/T-bone accidents is down 67 percent during the same time period, head-on collisions are also down 67 percent.

Background

A diverging diamond allows traffic to temporarily cross to the left side of the road. This design is intended to improve safety and mobility, and to move traffic more efficiently. It reduces the number of “conflict points” vs. a traditional four-way interchange. DDI motorists cross the interstate on the left, rather than the right side of the road, and then slightly bear left to enter the interstate, eliminating left turns in front of oncoming traffic.

When the Cornelius DDI first opened in 2014, it was one of only 48 in the nation. A decade later, there are some 280 DDI interchanges nationwide according to the Federal Highway Administration. The newest: Exit 23/Gilead Road in Huntersville.

Concerns

Despite a clear indication that the DDI design is safer than the traditional expressway entrance and exit, there are concerns.  Some motorists who are not familiar with the crossover aspect of the interchange find it confusing at first.

The DDI is also a challenge for emergency vehicles.

Cornelius Fire Chief Guerry Barbee

“Congestion on the DDI is a concern for our responding units,” said Cornelius Fire Chief Guerry Barbee. “But this can be found at multiple intersections throughout town, not just at the DDI.”

Going forward

A request has been made in the FY26 town budget for traffic preemption software that can be added to fire apparatus as well as traffic control devices that would allow for congestion to clear as the apparatus approaches the intersection, allowing for faster response times.

The Catawba Avenue DDI is hardly ideal. There should be a greater distance between the bridge and  Torrence Chapel Road/Liverpool Parkway on the west side of the interchange, and Statesville Road/Hwy. 21 on the east. This would provide more stacking room, reducing some of the congestion.

Unfortunately there appears little likelihood that those roads can be moved, although the addition of the dual roundabouts on Statesville Road east of the bridge, currently under construction, may eventually help.

Overall, however, the reduction in accidents and injuries suggests that the Cornelius Exit 28 DDI is here to stay.