Cable barriers on Minnesota freeways stop crashes, save lives
Simple steel sentinels will be on duty this Memorial Day weekend, protecting Minnesota motorists at minimal cost.
During a decade of service, they’ve done a sterling job, officials say. No fatal cross-median crashes have occurred where the cables are in place, said Kevin Gutknecht, communications director for the Minnesota Department of Transportation.
The first cable fence was installed in 2004 along Interstate 94 between Maple Grove and Rogers. Before then, that stretch had five fatal cross-median crashes, Gutknecht said. There have been none since.
“We install cable barriers where there is a high likelihood of crossover crashes, which are likely to be severe or fatal,” Gutknecht said.
Crash rates, speed and traffic volume are among the factors considered. Highway engineers also look at the width and slope of the median and future road construction plans.
Gutknecht said federal crash tests have shown that high-tension cable barriers are more than 90 percent effective in keeping vehicles on the correct side of medians.
“The statistics speak for themselves,” he said. “When a cable median barrier is installed, it reduces cross median head-on crashes almost completely. The cross median head-on crashes are often life-changing or fatal. The barriers are very effective and have saved lives.”
State Patrol spokesman Lt. Eric Roeske said it’s hard to quantify prevented crashes. But “every time they (cables) are hit, there is potential for a crossover crash,” he said.
Gutknecht said the best evidence of the 42-inch-tall barriers’ effectiveness is the damage they absorb: downed posts and cables that have kept out-of-control drivers from going across medians.
Cable barriers have been struck more than 440 times since 2009, when MnDOT began collecting such data. The resulting damage has cost about $498,000 to repair, Gutknecht said.
Cables in the Northland The state has 390 miles of cable fences, up from 116 at the end of 2008. In the Northland, cables start on Interstate 35 near Cloquet and continue south, off-and-on, toward the Twin Cities. MnDOT is adding additional cable barriers this spring in Pine and Carlton counties, and plans to add cable barriers from Cloquet toward Duluth later this construction season.
In Duluth and Proctor, the I-35 median is blocked by fixed guardrails and concrete barriers.
MnDOT says the cables cost up to $150,000 per mile to build, about a third of the cost of concrete barriers. The state spends about $7,000 per mile to repair damaged cable fences in the metro area. It recovers much of that from insurers of the vehicles involved.
One downside of the cables is that they often cause significant damage to vehicles whose drivers might have been able to regain control in a grassy or snowy median. But officials think that consequence is outweighed by what the cables prevent.
When an uncontrolled vehicle goes into the median, “the risk of crossing into oncoming traffic and causing life-changing injury or death is very high statistically,” Gutknecht said. “It’s a trade-off between property damage versus injuries and death. When there’s a head-on crash there is also property damage.”
How they work The cables are bolted to concrete anchors at each end to keep them taut. They are strung between steel posts, which slide into buried concrete sleeves.
When hit, the posts are designed to snap off and the cables flex outward with incoming cars, absorbing the kinetic energy. Then the cables swing back, forcing the vehicle back onto the highway shoulder.
A fairly simple fix Damaged fences are fairly simple to fix. New posts are slipped in for bent ones, and loose cables reattached and tightened.
Gutknecht said most barrier repairs take about 30 minutes in the summer and perhaps two hours in the winter because of cold-related complications.
He said MnDOT averages about five days to fix damaged barriers, weather permitting, and it didn’t permit much this winter when response time was longer. He said no vehicles have gone over downed cables into the median.
The cables are less effective when snow piles against them, sometimes making it possible for cars to jump the fence.
So after initial snow removal, plows return to push snow away from cables, as well as guardrails and other barriers.
This spring in Coon Rapids, there are about 10 spots along U.S. Highway 10 where shiny new cable posts have replaced damaged ones, evidence that they’ve seen action.
The cables “have had a significant impact on safety,” said Coon Rapids Police Chief Brad Wise. “Vehicles used to slide into oncoming traffic. That’s impossible with cables. They are saving lives.”