Cable barriers said to be preventing crossover accidents on Tennessee roads
By Steve Ahillen Knoxville News
If you think kudzu spreads fast in Tennessee, check out the growth rate on guard cables.
More specifically median cable barriers. Those endless stretches of thick wire three, sometimes four strands high were just about nonexistent four years ago but are now suddenly everywhere along the state's interstates and major roads.
The program started in 2005 on an experimental basis with short lengths around Memphis, Chattanooga and the Tri-Cities, but didn't really take off until 2008 when it was decided to go statewide and 200,000 linear feet was installed. Overall, 1.4 million linear feet has been installed in the state, according to Julie A. Oaks, spokeswoman for the Tennessee Department of Transportation, in an e-mailed response to News Sentinel questions.
"Over the past several years Lane Departure crashes have been a major cause of highway fatalities in Tennessee," wrote Oaks. "Crossover head-on crashes tend to be the most severe of the lane departure crashes. Systemic installation of median cable barrier rail is one main strategy to combat this type of crash."
"We hit every place that we knew we had crossovers (wrecks)," Steve Hall, TDOT's assistant chief engineer, said in a phone interview. "There could be a road safety report for some section of roadway that we may say, 'This is a good section for that.'
"What is so good about these barriers versus a concrete barrier or guardrail is that the cable is much more forgiving," Hall added. "Concrete doesn't give too much. The guardrail has a deflection in the neighborhood of 3 feet. These cables amount to about 8 feet and can deflect to about 10 or 12 feet. It stops the vehicle from crossing but doesn't impact the occupant as with concrete.
"It doesn't redirect the car as much," said Oaks. "The car or vehicle will actually get hung in it. The idea is to catch it in that fence."
Hall said most of the building has gone on in 2009-10 at a cost of $19 million to date - a large price tag but not nearly as expensive in construction or repair as the traditional concrete and metal barriers, Hall said.
The cost of repairing cable barrier rails is $5.50 per foot compared with $16 per foot for the typical guardrails, Oaks said.
"You can never prove that the car would have gone into the median but you had a good gut feeling that they would have," Hall said. "The Tennessee Highway Patrol says they think they (the barriers) are saving lives."
He mentioned a section of state Route 385 in Shelby County that had been the scene of several crossover fatalities. It was among the first to get the barrier rail and "we have not had any trouble at those locations since."
"I travel a route (Vietnam Veterans Parkway near Nashville) to work," Hall said. "We installed (barrier rail) there after three crossover fatalities. There have been no crossovers since."
Still, there have been problems and complaints.
Two workers were killed in November 2009 while installing the barriers on Interstate 75 in Anderson County north of Knoxville. Cheyenne Dakota Burke, 18, and Jeffery Brian Thompson II, 19, died instantly after being hit by a truck that had driven into the median.
The Arizona Department of Transportation came under criticism after media outlets documented fatalities on crossovers on stretches of highway where the cable barriers were in place. Contentions were that the barriers were installed hastily and incorrectly, placing them in areas where their value was limited.
"We reviewed literature and talked to other states about what they were doing," Hall said. "Some states, like North Carolina and Missouri, got out early in this."
"TDOT let some of the other states go first to see how they were going to work out," Oaks said.
The department learned, for example, that the cable isn't the answer everywhere.
"We try to keep them in a flatter area where the slopes are not more than 6-to-1 (ratio)," Hall said. "They (cars) will go under them (if the nose of the car is headed down a steep slope)."
Because of this, Hall explained, the barriers are not put up in the middle of medians, which are usually at the bottom of slopes created by the roads built up on either side.
"Ours are roughly 8 feet off the shoulder," he said. "If we have to replace a long run, we are looking at moving it a little farther to 10 feet from the travel lane."
Motorcyclists had complained in letters to The Tennessean, Nashville's newspaper, and elsewhere that the cables could produce some grisly accidents for cyclists and had suggested moving them farther from the road.
Hall said that although most of the barriers have been installed, TDOT is not above tweaking the system.
For example, the department has decided to go from three strands of cable to four, although three strands meet Federal Highway Administration requirements.
"This will take care of a larger vehicle like a FedEx truck," he said, adding that four strands of cable reduce the chance of vehicles going under the barrier.
In September, TDOT decided to operate the program under separate contracts than those for other highway safety maintenance. This was done, Hall said, because the cables were not getting repaired quickly enough. Documentation provided by TDOT shows four contracts awarded in September for a total of $2,299,319.07 for repair of cable barriers.
"We have shortened our repair time to seven days. Once we receive a call, they have seven days (to repair it)," Hall said.
Keeping up with repairs is still a challenge. "Sometimes there is downtime before they get reported," Hall said.
Toward that end he asked that anyone noticing places where the barriers have been knocked down report them by e-mail to TDOT.Comments@tn.gov or by calling 1-877-SMARTWAY.
Oaks said TDOT is using the Tennessee Executive Leadership Academy - a group created within TDOT to help ensure future leadership for the department - to evaluate how well the barriers are working.
"They will be looking at the number of times the barriers are hit, the public perception, crash records, etc.," said Oaks. "Basically it will be a comprehensive look at the system. Instead of spending a lot of money on (outside firm) evaluation, we are using the leadership academy."
She said that in the past the academy was used to evaluate such projects as petroleum use, environmental conservation and emergency response.