The highway project well under way along Interstate 40 in eastern North Carolina was not undertaken to move traffic faster or to lessen highway congestion. The goal was simpler than that — and more important. The purpose is to make travel safer.
The contract awarded to Barnhill Contracting Company had sort of a perverse goal, actually. The contractor was to be paid for taking a smooth stretch of interstate highway and making it a tiny bit rougher.
Specifically, the contractor was to overlay 80 kilometers (50 mi.) of the roadway from a point east of Newton Grove through Duplin and Sampson counties and into the western edge of Pender County.
This is low-lying country, with wetlands sometimes on both sides of the road and water standing in roadside ditches. It is far enough east that signs in Pender begin to advertise the ferries that serve North Carolina coastal communities and tourists passing through them.
This last leg of eastern I-40 pavement was opened in the 1990s. The highway is a conduit for residents in the central part of the state who want to reach quickly the state’s southern coastline. Business people and students also contribute to traffic, heading to Wilmington’s university campus or various industries.
The problem is that this flat, smooth and busy stretch of Interstate 40 is subject to hydroplaning, which is where tires lose their traction to pooled water and slide out of control, sometimes carrying a vehicle across a median and into the path of oncoming traffic.
To begin to rectify this hazard, Bruce Taylor, area asphalt manager for Barnhill, oversaw the laying of nearly 2-centimeter (.75 in.) thick open-graded friction course. This asphalt product contains no sand, the asphalt compound instead relying upon small stone, polymers and a special fabric.
The combination of materials is said to pull down water into the top strata of pavement, rather than let it pool on top to loosen a tire’s grip. The coarse pavement also reduces dangerous sprayback, which is the curse of drivers following tractor trailers.
“The fabric helps prevent the liquid from dripping off the aggregate,” Taylor explained. This “drain down” effect lets water gravitate outward to shoulders of the road.
Taylor used a Blaw-Knox 3200 series asphalt paver to lay the friction course atop existing asphalt pavement. In all, 54,900 metric tons (61,000 tons) of the asphalt mix were laid over 80 kilometers (49.7 mi.).
The material was hauled to the site from the Barnhill bulk plant at nearby Kenansville, one of nine plants the company operates in the state. The mix was transported in company-owned quad-axle Sterling trucks, each with a capacity of nearly 20 metric tons (22 tons).
Creating this coarser, more porous surface was just part of the safety project. The rest of the nearly $8-million contract has a subcontractor working between the pair of two-lane roadways, in the narrow median that separates traffic flowing in opposite directions.
In the fall of 1998, North Carolina Department of Transportation (NCDOT) officials embarked on a statewide initiative to reduce cross-median fatal accidents. The goal of the four-year program was to erect 1,580 kilometers (990 mi.) of barriers of four-lane roadways with medians no wider than 2,100 centimeters (70 ft.). In 1999, 320 kilometers (200 mi.) of the work was finished.
The mix of barrier types ordered by DOT includes a cable-post combination that has proven effective. It was designated for the stretch of I-40 Barnhill worked on.
“Some events [accidents] there brought it to our attention that during heavy rain there was a problem,” said Tony Wyatt, NCDOT traffic safety engineer.
Reynolds Fence and Guard Rail Company of Indian Trail, NC, won the Barnhill subcontract to erect the barrier. Reynolds’ part of the contract actually runs 43 kilometers (27 mi.) farther east of where the paving work ends.
The barrier is comprised of three horizontal cables affixed to 2.25-kilogram (5 lb.) H-posts. The posts are a little more than 150 centimeters (5 ft.) in length. They are pounded 60 centimeters (2 ft.) into the ground at a spacing of 480 centimeters (16 ft.) on center.
The seven-strand steel cable is characterized as “pretty stiff” by Jack Reynolds, president of Reynolds Fence. Two of the cables are affixed by U-clamps to one side of a post and the third cable is attached to the other side.
The cables span distances as long as six-tenths of a kilometer (.4 of a mi.). At their ends, the three cables are pulled down to ground level and bolted to a steel turnbolt in which is integrated a stiff spring 30 centimeters (12 in.) long. The bottom end of the turnbolt is connected to a buried steel anchor.
This configuration produces a taut barrier with built-in give. In fact, the cable will deflect 330 centimeters (11 ft.), stopping a vehicle slowly or bouncing it away instead of bringing it to a smashing, deadly halt.
Before this job is through, Reynolds’ crew will stretch and anchor 122,070 meters (409,000 ft.) of cable. All of it will be unrolled from a reel that holds up to 600 meters (2,000 ft.) of cable. The reel is attached to an A-frame mounted on a trailer and is controlled by an air brake.
The cable-and-post system was first used in North Carolina three years ago. At that time, some “horrible accidents’ were happening on the leg of I-40 that runs west from Raleigh to its airport. In response to the deaths, DOT officials quickly erected two runs of the cable-and-post barrier on the median between the three- and four-lane freeways. The project was a success.
“The barriers took a beating, but they really stopped the cross-median fatalities,” Wyatt recalls.
The barrier used today evolved from similar systems first used in New York and California. Its installation depends upon several criteria — median width, slope of embankment from a shoulder, roadway curvature and existing physical features.
“It is a relatively inexpensive, quick to install, forgiving median barrier system,” Wyatt said. But its “forgiving” nature also means it is easily abused by hurtling vehicles.
Reynolds remarked that when he sees a stretch of the barrier with broken posts and slack cable, he realizes another car has been saved from crossing the median into deadly onrushing traffic. The posts are replaced in such instances, and the cable retightened.
Wyatt agrees that the flexible barrier is effective because it is not indestructible. “By being such a forgiving system, there have been lots of drive-aways after accidents,” he said. “But it does involve a good bit of maintenance.”
Some effort is taken to reduce at least some maintenance — by DOT median mowing crews: slow-growing sod called “centipede” is planted in the area directly beneath the cable-post units.
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