A&P Services of Asheville, N.C., is installing the cable barrier system manufactured by Gibraltar Cable Barriers L.P., Marble Falls, Texas.
A construction project is under way in Virginia’s Allegheny County on a section of highway about five miles in length, stretching from mileposts 19 to 24 on Interstate 64 that will improve safety conditions by protecting motorists from cross-over collisions between eastbound and westbound traffic.
Some years ago, the material of choice for a barrier system may have been concrete barriers, but many states are now looking to cable systems that provide a sort of safety net that helps keep vehicles on the right side of the median without the high crash impact of a cement barrier. They also are a less expensive option.
The safety improvements on I-64 have been taking place for nearly a year. Before the cable system could be installed, the inside shoulders needed to be reconstructed and the drainage system needed to be improved.
Branch Highways Inc., Roanoke, Va., is the prime contractor on the job. Greg Suttle is Branch Highways’ general superintendent and is currently filling in for the project manager. According to Suttle, Branch Highways was running three pipe crews working on the drainage system during the past year. Each pipe crew had an excavator, loader and truck. These were a mixture of John Deere and Caterpillar equipment. Branch owns its own fleet of equipment for doing such work, but some of the equipment was rented, such as the zero-turn excavators. These were rented because the company normally does not use that type of equipment.
“We’ve installed all new drainage throughout the entire five-mile corridor,” said Suttle.
“For that we used head-zero turn radius machines, working one half of the road at a time. These had a reduced swing radius so they won’t swing past the tracks. They were 225 size, and capable of picking up 12,000 pounds.”
Over one mile of pipe was used on the job. The function of the pipe is to either drain the median or let water drain from one side of the road to the other so it doesn’t build up on top of the highway. Most of the polyethylene pipes averaged about 24 in. (61 cm) in diameter. The largest of the pipes were 42 in. (107 cm) in diameter, and the smallest pipe on some of the side roads was 15 in. (38 cm) in diameter. The drainage pipes were the backbone of the project according to Suttle, and also were the most time-consuming item of work out on the job site. But in the end this fairly narrow section of interstate should be much safer and have better drainage.
A double run of cables is being done because Branch only wanted 9-ft. (2.7 m) deflections and the roads are so close together. Branch could not get a 4 to 1 slope in behind it so there had to be two runs of cable.
“If you had a little bit wider, flatter median there you probably could have gotten by with one cable system there,” said Suttle. “But even with doing a double run of the cable barrier systems, it’s still cheaper than using concrete for this median project.
During the past year the work site has averaged 20 to 25 Branch Highways employees. The company also has about 12 subcontractors on this job and five major suppliers. These include contractors doing the asphalt work and the highway striping work. The striping alone accounts for nearly one million dollars of the cost of the project. This includes the striping on a service road running parallel to the interstate being worked on. Other contractors include surveyors, truckers, and pavement groovers. The total cost of the project is $10.6 million.
“This was fairly typical interstate work. On one side road it’s an industrial area. There are two schools on the side road and we were limited in our flagging there. We had to get out of the road at two in the afternoon and could not start until 8:30 or so.”
The installation of the median cable barrier system has now started. A&P Services of Asheville, N.C., is installing the cable barrier system manufactured by Gibraltar Cable Barriers L.P., Marble Falls, Texas. Gibraltar’s main product is its highway safety barrier. The company also produces an anti-terrorist barrier system product. Its highway product is a life-saving barrier designed to contain and re-direct out-of-control vehicles from crossing the median into oncoming traffic. According to Jay Winn, Gibraltar regional sales manager, it works the best when installed on long stretches of highway when entrance or exit ramps are involved.
“There is a place for all three barriers, concrete, guardrail and cable barriers,” said Winn. “Concrete is expensive but is effective for very narrow medians. But impacts can also be quite deadly. On guardrails there can be snagging involved and issues with the changes in designs of cars over the years, making the guardrails, designed for impact of older vehicles, now obsolete.
“Cable barriers are soft and flexible, providing less damage to the vehicle and less injuries to the occupants. But you also need the space in the median for them to be effective. It can be placed on slopes without bringing in a lot of dirt. Testing has been done for up to a 4 to 1 slope. Any more than that is too steep. The barrier works best when installed close to the shoulder.
“It is simple to repair. After a collision, the cables are typically still up because there is tension on them. New posts are simply slid back into the base. Each cable is at a specific height for a range of vehicles. The bottom cable catches the bumpers of most small cars. The next cable up will engage the bumpers of most SUVs and pickups. The top cable, at 39 inches is for cargo trucks, similar to the height of a semi. Testing was done for an 18,000-pound cargo truck. We have stopped semis,” said Winn. “But we haven’t tested for that and would never advertise for this ability.
“Our longest strand, from anchor to anchor, is about 36,000 linear feet. There is a single anchor (pier) at either end holding the tension. The cable is supported by the posts/parts, keeping the cable up at design heights. Generally, there is 4,000 to 6,000 pounds of tension on each cable, and that goes up in the winter.”
“As far as challenges that’s a darn rock pile up there,” said Kevin Glenn, project manager of A&P Services LLC. “Evidently, a long time ago there were coke ovens up there and a lot of their waste went down into the roadbed. As a result, we also are having to use drilling equipment on a portion of it to get through the layers of slag and whatever other stuff that was put down. We’re actually having to drill up some old metal tailings too.”
A&P Services is putting up 11 mi. (17.7 km) of the cable barrier system.
“This is only the second high-tension cable system in Virginia,” said Glenn. “The first one is up in Harrisonburg, Virginia. We’re running a six-man crew to install this cable; that includes me. We use our standard guardrail equipment to put that in. We have figured that this installation will take us about two and a half months total work time. We don’t get involved in design at all; we simply go with the specs we are supplied with.
“This is unusual for us as it is a new product. But there are hundreds of miles of it throughout the country now and we’ve talked to other installers who have dealt with it and we’re OK with it. We do guardrail. That is our specialty and we have been working up in Virginia for about seven years now.”
Glenn has 40 years of experience in doing this type of work. A&P Services has been in business since 1995. Glenn was a Connecticut guardrail contractor for a long while prior to his working out of North Carolina.
“I believe they have been installing this for about six years nationwide now, not much longer than that and there is always that initial hesitation to try a new product,” said Glenn. “But it is guardrail, putting posts in the ground — the basic idea hasn’t changed much over the years, although the cable barrier system concept and technology has now really taken off and is a good thing.”
The high-tension wire rope barriers are the newest version of cable barriers, which started out as low-tension barriers. The low-tension system has a higher percentage of penetrations by virtue of its greater flexibility, due to lower tension, according to Winn, after a hit, the cables lay on the ground until repaired, and are more expensive to repair.
The cable barrier is installed right at the edge of the shoulder. There also is a median ditch that is 10 to 12 ft. (3 to 3.6 m) wide behind the cable system. It’s only 16 in. (41 cm) from the edge of the cable barrier to the ditch.
They hope to finish this job up in October even though it is officially scheduled to end in December. The weather has been pretty good for construction up until spring of 2011. This year has proven very, very wet. In the contractor’s favor was the fact that it was doing work on an already-paved surface and the weather did not affect crews as much as it did a lot of other contractors on jobs in the area who were working directly on the dirt.
“We missed about five days out of the month,” said Suttle. “They missed 20."
The goal of the project is to improve safety conditions along this portion of I-64 and Winterberry Avenue. By reconstructing the inside shoulders, improving the drainage in the area, and installing high tension cable guardrail in the median of Interstate 64 and between westbound I-64 and Winterberry Avenue, motorists should have a much less threat of cross-over collisions between eastbound and westbound traffic on these routes. CEG