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Is Wake Forest Road at the Beltline a good place for a 'diverging diamond?'

New interchange considered to ease Wake Forest Rd - Beltline traffic

Nearly 75,000 vehicles are expected to pass through the Wake Forest Road interchange with the Beltline each day in 2040, and NCDOT planners think crisscrossing traffic might be the best way to handle them.
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Nearly 75,000 vehicles are expected to pass through the Wake Forest Road interchange with the Beltline each day in 2040, and NCDOT planners think crisscrossing traffic might be the best way to handle them.

Nearly 75,000 cars and trucks are expected to pass through the Wake Forest Road interchange with the Beltline each day in 2040, and state highway planners think the best way to handle them is with a new kind of design that involves crisscrossing traffic.

The N.C. Department of Transportation is proposing to convert the interchange to a "diverging diamond." Traffic on Wake Forest would cross to the "wrong" side of the road at traffic lights on either side of the Beltline underpass, eliminating left turns and the amount of time drivers spend sitting at red lights.

NCDOT engineers will present their plans, answer questions and get feedback at a public open house at the North Raleigh Hilton on Thursday evening.

The N.C. Department of Transportation made this video to explain the "diverging diamond" interchange or DDI. The department is planning to build two of them in the Triangle, at the Beltline and Western Boulevard in Raleigh and at Interstate 40 and

The Wake Forest interchange is among a handful of places in the Triangle where NCDOT engineers think diverging diamonds would improve traffic flow. Others include the Western Boulevard interchange with the Beltline and the junction of Interstate 40 and N.C. 42 in the Cleveland community of Johnston County.

But unlike those two projects, NCDOT does not plan to build a new bridge at Wake Forest Road.

"We are not proposing any changes to the bridge that carries I-440 over Wake Forest Road," Meredith Van Duyn, an engineer for the consulting firm RS&H, told the Midtown Raleigh Citizens Advisory Council this winter. "It's in good condition."

That will present some challenges, as designers attempt to maintain six travel lanes and four turn lanes under the bridge, plus add the median that would keep the two sides separate. Also, while pedestrians and cyclists are often routed down the middle of diverging diamonds, to minimize crossings, that can't happen here because of the piers holding up the Beltline bridge, Van Duyn said.

Instead, pedestrians and cyclists remain on the outside of the travel lanes along the bridge abutments, which are sloped now and would have to be rebuilt to be vertical to provide more room.

In addition to speeding the flow of traffic through the interchange, a diverging diamond is designed to be safer, by reducing the number of "conflict points" — the places where cars have a chance of colliding. The diverging diamond would have 14 conflict points, Van Duyn said, compared to 26 for the traditional interchange there now.

Diverging diamonds have been met with skepticism in the Triangle, in part because on paper they look daunting. But those who have driven through ones elsewhere in the country say they are easy to use if you follow the signs and the road.

"It won't be as confusing as some people think," Van Duyn said.

The open house will take place from 4 to 7 p.m. Thursday, May 17, at the North Raleigh Hilton, 3415 Wake Forest Road. There will be no formal presentation, and people can come and go as they please.

NCDOT will accept feedback on the project from the public through June 1. To submit a comment after the meeting, contact NCDOT project manager Ahmad Al-Sharawneh at aalsharawneh@ncdot.gov or 919-707-6010. or VanDuyn at 919-926-4102 or meredith.vanduyn@rsandh.com.

Richard Stradling: 919-829-4739, @RStradling

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