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Exit 28 DDI demolished crash rate in first six months

Exit 28 DDI demolished crash rate in first six months

June 5. By Dave Vieser. Although the construction of the Exit 28 Diverging Diamond Interchange (DDI) generated plenty of controversy, the payback appears to be a safer interchange. According to town officials, traffic accidents at the interchange fell 58 percent during the first six months we’ve been diverging on the diamond.

For town and state officials who emphasized the better safety record of existing DDI intersections in other parts of the country, the new figures are heartening.

“We looked at a six-month period prior to construction beginning, and then a 6-month period after construction was completed,” said Assistant Town Manager Andrew Grant. “The results: Pre-DDI: 19 crashes, post-DDI: Eight crashes. That’s a 58 percent reduction.”

Grant said that the town will continue to carefully analyze the crash figures in coming months but that the initial results were encouraging.

Part of the reason for the reduction is that the DDI traffic flow pattern reduces the number of conflict points when compared to a traditional interchange design.  “Since the DDI, there have been no accidents that involve vehicles turning left in front of oncoming traffic, which are normally more severe accidents,” Grant said. As a result, there have also been fewer injuries in those accidents which have occurred.

In other news involving the DDI:

  • The State DOT has installed “No Turn on Red” signs for motorists exiting I-77 at Exit 28, after determining that drivers seeking to turn right onto Catawba had insufficient sight distance for safe movements. There were no such prohibitions for right turns on red under the intersection’s previous configuration, but apparently state officials felt that the curve in the roadbed installed as part of the DDI prevents motorists from seeing oncoming cars.
  • Uncertainty regarding the I-77 widening has brought all unfinished aesthetic work on the DDI to a halt. “It would make no sense to do anything more at this point, only to have to tear it down,” said Town Manager Anthony Roberts during his June 1 budget presentation to the town commissioners. “Everything is on hold at this time.”
  • A bill introduced by State Sen. Jeff Tarte which would have permitted left turns at steady red signals in DDI’s appears to be going nowhere this session. It was referred to the Senate Transportation Committee in late March, and there’s been no action since. Efforts to reach Tarte were unsuccessful.
  • Studies are about to begin concerning the future of the intersections of Catawba at both Hwy. 21 and Torrence Chapel Road, sometimes referred to as the “bookend” intersections. “The implementation of the new DDI traffic pattern has greatly improved traffic flow at the interchange itself, but 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,” said Grant. “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.”
  • Grant said that the engineering and construction drawings for the 21 Roundabout project are about to get under way, and that the town and DOT will soon begin a study of the Torrence Chapel/Catawba Avenue intersection to determine the best design alternative. However, completion of those projects will be at least a few years away.