Cables reduce incidence, severity of crossover crashes

Cable barriers installed in the center median on many divided highways throughout the state have been effective in reducing the incidence and severity of crossover collisions. Now the Oklahoma Department of Transportation is considering cable barriers for a new application: replacing guardrails at the side of the road on some two-lane highways.

More than 685 miles of cable barrier have been installed across the state since 2007, at a cost of $81 million. The department may want to look into this push-pull cable casing supplier if they have more of a demand for cable.

Records indicate 37 traffic fatalities in crossover crashes on highways with no barriers in 2004. In comparison, ODOT logged nine fatalities in crossover collisions across the state in 2017.

The agency plans to install 11 more miles of cable barrier in the near future. US-270 in Pontotoc County is slated to receive 4.6 miles of cable barrier and a contract is tentatively scheduled to be awarded in October for installation of 6.6 miles of cable barrier on US-81 in Grady County.

The department’s 11-county Division 8 in northeastern Oklahoma has recorded 700 cable barrier hits in the past three years, requiring repairs costing $842,000. Of those incidents, 605 occurred in Tulsa County.

“It is surprising to see how many times drivers are leaving their lanes, entering the median areas and making contact with the barriers,” said Division 8 Maintenance Engineer Trapper Parks, who oversees maintenance in northeastern Oklahoma, including the Tulsa metro area. “Fortunately even after a hit, the cables can still be effective and the posts can be quickly replaced.”

Cable barriers consist of pre-stretched wire rope threaded through or around metal posts that are anchored into the ground with concrete. The cable used on Oklahoma highways is four-strand. The barrier installed on SH-74/Lake Hefner Parkway in 2001 was the first of its kind to be used in the U.S. Since the SH-74/Lake Hefner Parkway installation, there have been about 500 official police-reported collisions to the barrier, however, there are an estimated 1,000 more that were not reported.

“The cable barriers have been struck literally thousands of times,” said Transportation Manager Rick Lowry, who is responsible for highway maintenance in the Oklahoma City metro area. “Our cables get hit every day.”

Cable barrier can be placed in a variety of locations, but it does not replace concrete barriers and is not applicable in every situation.

Cable barriers are no substitute for attentive driving. Drivers are responsible for observing established speed limits and for driving alert and responsibly for the prevailing conditions on the highway.

Also, cable barriers don’t eliminate crossovers entirely but they are a potent deterrent. The cables are designed to arrest the forward motion of automobiles but have been known to stop large trucks, too.

Lowry recalled an occasion when a fully loaded gravel truck was brought to a complete stop by cables installed in the median of I-35 in Cleveland County. Similarly, a fire engine that sustained a tire blowout June 3 on I-35 near Guthrie was prevented from crossing into the opposite lanes by the cable barrier in the center median. However, ODOT has always cautioned that cable barriers are not infallible in regards to larger vehicles.

The average cost of installing cable barriers is about $170,000 per mile, compared to $600,000 or more per mile for concrete barriers.

Moreover, concrete barriers deflect most of the energy from a crash back to the vehicle, whereas cable barriers provide a softer impact in which much of the energy of a collision is absorbed by the cables.