Here’s how a diverging diamond interchange works
As Creedmoor Road heads north out of Raleigh and passes under Interstate 540, it quickly narrows from a four-lane divided boulevard to a two-lane country road with a speed limit of 55 mph.
Now the N.C. Department of Transportation has drafted plans to widen Creedmoor, also known as N.C. 50, to four lanes between I-540 and N.C. 98. The public will get a chance to see them Tuesday evening during a meeting at the Amran Shriners temple at 11101 Creedmoor Road.
The goal is to improve safety and traffic flow along a busy road for commuters both coming south to Raleigh and Research Triangle Park and going north to Granville County, where state and federal institutions in Butner employ thousands. Some legislators have proposed moving the headquarters of the state Department of Health and Human Services to Granville County.
Granville County leaders have for years agitated for N.C. 50 to be widened, to help commuters and to bring the county closer economically to the Triangle. For now, NCDOT is proposing only to widen the busiest five-mile stretch closest to I-540, which carries about 20,500 cars a day, according to the state’s latest estimates. Justin Jorgenson, Granville County’s senior transportation planner, says it’s a good start.
“Ultimately, we’d like to see more improvements,” Jorgenson said. “But we’re absolutely thrilled with this project. Getting it widened to N.C. 98 is a big achievement.”
It will also mark the first time a four-lane road will extend deep into the Wake County portion of the Falls Lake watershed, the area that drains into the county’s largest source of drinking water.
Concern about how a four-lane highway might spur development and harm the lake has helped to blunt any urgency to widen N.C. 50 north of Raleigh over the years. In 2011, state and local planners came up with a strategy for improving N.C. 50 in stages and with an eye toward protecting the lake and the rural character of the highway.
The section to be widened is still about a mile and half south of Falls Lake, reducing concerns that construction or highway runoff would directly harm the drinking water supply, said Tim Gardiner, a transportation planner for Wake County. The Army Corps of Engineers and other regulatory agencies will work with NCDOT to try to prevent runoff from reaching the lake, Gardiner said.
“They feel like this project can be done without any direct impacts to the lake,” he said.
NCDOT’s plans call for a road that would require less space than a typical rural four-lane highway. Rather than a wide, grassy median, traffic will be separated by a raised median, keeping the road’s footprint more compact.
Public feedback sought
NCDOT has developed two options for widening the highway. The first calls for three traditional intersections with traffic lights at Norwood, Mount Vernon Church and the confluence of Nipper and Shooting Club roads, which would be realigned to meet head-on.
The second plan would replace those traffic signals with what traffic engineers call “reduced conflict intersections,” which would prevent drivers on the side roads from crossing N.C. 50. Instead, they would have to go right onto N.C. 50 and turn around at a designated U-turn area to head back to the intersection.
NCDOT is also considering two options for the I-540 interchange. One would involve tinkering with the current design, while the other would replace it with what’s known as a diverging diamond, a concept that’s still new to the Triangle. Engineers say diverging diamonds reduce crashes and work more efficiently by crisscrossing traffic at either end of the interchange in a way that eliminates left turns and the amount of time drivers spend sitting at red lights.
Allison White, NCDOT’s project manager, said the department will craft a final plan based in part on the feedback it receives from the public. In addition to Tuesday’s meeting, which runs from 4 to 7 p.m., people can comment online at publicinput.com/NC50-Creedmoor-Rd.
NCDOT expects to begin acquiring property it needs to widen N.C. 50 sometime in 2021, but construction isn’t scheduled to begin until late 2024, White said. The current budget for the project is about $92.3 million.