Forsyth County Shines With Diverging Diamond Interchange

Mon July 07, 2014 - Southeast Edition
Eric Olson


Larco’s paving equipment stands ready for use on the new lanes of Union Cross Road in front of Caterpillar’s axle manufacturing plant.
Larco’s paving equipment stands ready for use on the new lanes of Union Cross Road in front of Caterpillar’s axle manufacturing plant.
Larco’s paving equipment stands ready for use on the new lanes of Union Cross Road in front of Caterpillar’s axle manufacturing plant. Crew uses a Komatsu PC360LC excavator for work at the site of the existing bridge over I-40. Traffic moves along I-40 and under the new bridge that carries vehicles up and down Union Cross Road.

With summer in full swing, road crews are expected to ramp up the rehabilitation of a 4.2-mi. (6.8 km) stretch of Union Cross Road in eastern Forsyth County that will include the area’s first diverging diamond interchange, or DDI, at its intersection with Interstate 40.

The $30.3 million project first began in the spring of 2012. Work crews have been busy since then widening the old two-lane road to four and five lanes from Sedge Garden Road just north of I-40 to just south of U.S. Highway 311, an interstate-like four-lane route that connects Winston-Salem to High Point.

Larco Construction, a division of Branscome Inc., a general contractor based in Williamsburg, Va., is overseeing the project. When finished, Larco projects that it will have placed almost 200,000 tons (181,436 t) of asphalt and moved 260,000 cu. yds. (198,784 cu m) of excavated material at the work site.

An Area Transformed

The stretch of Union Cross Road that is seeing the construction is one of Forsyth County’s most high-profile growth areas and, indeed, this is the main reason for the road work. Over the past several years, the Union Cross Road area has been transformed from quiet farmland to what is now a home to several big-name manufacturing plants.

A Dell Computer factory was located just off Union Cross Road on Temple School Road for four years before the plant closed in 2010 due to lagging desktop computer sales.

Today, Herbalife, a global nutrition company, has taken over the old Dell factory and plans to open a 585,000-sq. ft. (54,348 sq m) manufacturing and distribution plant employing more than 500 people later this summer.

Add to that a nearby 850,000-sq. ft. (78,967 sq m) Caterpillar axle manufacturing plant, as well as various other employers, and the need for a wider Union Cross Road to handle the extra traffic becomes obvious, according to Wright Archer III, district engineer for the North Carolina DOT.

According to the NCDOT, 25,000 cars travel along this particular stretch of Union Cross Road daily, but that number is expected to increase to 41,000 a day by 2031.

“Traffic has really picked up in the last several years up and down Union Cross Road as all this new industry has gotten established,” Archer said. “Caterpillar has that huge plant there that makes axles for their mining equipment and they have been a big user of the road with large, heavy trucks coming through the area.”

Archer also pointed out that traffic is impacted by the presence of Glenn High School, located just a few blocks south of I-40.

“Well, with the industry and the school, as well as the natural growth of the area, it really is a high-growth area,” Archer said. “There are also new home developments going up out there as a result of the economic recovery. Even though there is still a lot of vacant farm land there, I think a lot of that will gravitate toward more development.”

A Good Intersection for a DDI

All of this new traffic on Union Cross Road is most apparent in the mornings and again in the late afternoons, Archer said. That is why the site of the bridge over I-40 became such a good candidate for the construction of a DDI.

Initially, plans called for a standard single-point interchange at the intersection similar to the wing-shaped overpass at I-40 and Gallimore Dairy Road several miles to the east in Greensboro.

“But we started looking at the age and the sufficiency rating of the bridge at Union Cross Road, which was very good, so we then decided to change the design to incorporate a DDI design,” Archer said.

A DDI is a type of diamond interchange in which the two directions of traffic on the road cross to the opposite side on both sides of the bridge at the interstate. It is unusual in that it requires traffic on the overpass (or underpass) to briefly drive on the opposite side of the road from what is customary.

In order to build a DDI at the Union Cross/I-40 site, a second overpass has been built that parallels the existing span. When the DDI is completed, traffic in both directions will cross from one bridge to the other over the interstate. Each end of the DDI will have traffic lights designed to control that traffic.

Archer said that the DDI will provide drivers with easier access to I-40 and help eliminate the congestion and accidents that occur when cars and trucks back up on the ramps.

“A DDI is needed at that intersection because in the morning and evenings there is a lot of left-turn traffic — a lot of opposing traffic — so if you have a couple cars trying to make a left turn, as well as straight through traffic, it really was locking up that single bridge,” Archer said. “That is what is unique about the design for the DDI at that site: If you are coming off I-40 and you want to make a right turn you kind of have a free-flow right. If you want to make a left turn, you are signalized but you almost have a free-flow left turn also. Your opposing movements are freed up to where you are under signal control on each end of the DDI. It is a little bit easier to manage and manipulate traffic when you have a heavy volume.”

The DDI at Union Cross Road and I-40 is one of several that are planned for North Carolina, most of which are at intersections at interstate highways. The innovative design is relatively new, with the first DDI in the United States installed in Springfield, Mo., in 2009. Popular Science magazine listed the DDI as one of the best innovations that year (engineering category) in “Best of What’s New 2009.”

Warm, Dry Weather Needed

Archer said that the new overpass at I-40 is about 90 percent complete and with warmer, drier weather the grading of the approaches to the bridge will commence.

Wet weather last summer and again over the winter has been the only real problem that road crews have faced on the project, according to Archer. Earthmoving came to a virtual standstill over the winter as a number of days were lost to bad weather.

Still, the project is on track, he said, for completion in November 2015.

With all the focus on the project’s unique DDI over I-40, Archer said that most of the work so far has been concentrated at Union Cross Road’s interchange at U.S. 311.

“We still have work to do there but we have been moving north toward I-40,” he said. “There hasn’t been a lot of work on the north side of I-40 toward Kernersville but that is going to pick up during the spring. That will primarily be widening and there will be some drainage work and signal work, also.”

Archer added that quite a bit of night work was done last year to install the cross line drainage over I-40 due to the high traffic volume during the day and he anticipates more night work closer to Kernersville in the coming months.