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Cornelius News

The DDI is still underwhelming, but it’s ridiculously safer


Oct. 13. By Dave Vieser. There has been a 40 percent reduction in accidents at the Exit 28 interchange in Cornelius since the Diverging Diamond Interchange debuted in 2014. Head-on collisions have been eliminated.

Town officials attribute the better safety record primarily to the reduction in the number of traffic conflict points when compared to a traditional interchange design. In the DDI design, motorists cross the interstate on the left, rather than the right side of the road, and then turn left to enter the interstate.

“Comparing calendar year 2013 (pre-construction) to calendar year 2015 (post-construction), there was a 40 percent reduction in total number of all types of crashes,” said Assistant Town Manager Andrew Grant. “More importantly, there was a 45 percent reduction in crashes with injury from 2013 to 2015.”

There has been a 78 percent reduction in angle crashes and a 56 percent reduction in rear-end crashes.

The report says there has been a 100 percent reduction in head-on crashes, as well as wrecks that involve a left turn.

DDI designs are less expensive than a full rebuild in that the existing bridge structure and the existing rights-of-way are utilized.

Nevertheless, even with the enhanced safety statistics, the Exit 28 DDI is still prone to congestion due to the “bookend intersections” at Hwy. 21 to the east, and Torrence Chapel Road to the west.

“We’ve known for years that in order to improve the traffic flow in the entire area, improvements would be needed at our bookend intersections too” Grant said. “The close proximity of the bookends to the interchange and the large volume of traffic in the area during all times of the day causes periodic back-ups into the DDI itself.”

That’s why an additional left turn lane is being added for eastbound traffic seeking to go northbound onto the interstate. Design work is also underway to make other improvements which will make the DDI even more efficient in the future.

Meanwhile, the town appears to have given up on finding a way to somehow improve the “mast and sail” design that was tacked on top of the DDI superstructure.

The plan was to create a sense of place what looked like a suspension bridge. The governor was supposed to come for the dedication of the bridge, but it became the subject of ridicule instead, spawning a Facebook page called Exit 28 Ridiculousness.

In the works is a $38,880 plan to improve the hardscape and landscape design. Design and development is under way now, completion is set for June of next year. Local design company ViZ LLC got the contract at the Cornelius Town Board meeting Sept. 6.

“This contract with Viz, LLC, whose Principal owner is Gary Fankhauser, is for design, bid services, and construction administration services for landscaping elements in the four quadrants of Exit 28,” said Assistant Town Manager Andrew Grant. “The scope of services includes developing sketch design alternatives, schematic design, construction drawings, technical specifications, working with NCDOT for permitting, bidding services, and construction administration services.”

Under the proposal, a final design would be presented to the town by December, and all work would be completed by the end of June, 2017.