How effective is freeway median cable barrier?

The in basket: John Rosinke of Silverdale wrote me on July 10 to say, “Read your column today and proceeded down the page to the Code 911 section. Noticed a pickup truck was able to cross the cable barriers on Route 16. Seems like I read several other reports that vehicles do cross cable barriers. Aren’t they supposed to prevent crossing to the oncoming lanes?”

The accident in question led to the death of the man whose pickup truck crossed the barrier.

I can recall reading of only one other such accident, also a fatality, but I’m sure there have been others.

I asked the state about the reliability of cable barrier in keeping out-of-control vehicles from crossing the median into the oncoming lanes.
The out basket: Claudia Bingham Baker of the state highway department said, “Yes, we do look at the conditions surrounding collisions in which vehicles breach cable barrier. We promptly repair the cable barrier when hit, and we also do annual inspections of the cable barrier to ensure it is in good working order and at the proper tension.

“A little background on cable barrier might be helpful. Cable barrier, like all barrier, is not designed to prevent all collisions. It is designed and built to certain criteria. When vehicles exceed those criteria with speed, momentum, angle of impact or other factors, cable breaches can and do occur.


“(This state) has been using cable barrier in various locations since about 1995. Over a three-year period in the mid-2000s we did formal performance reviews of the efficacy of cable barrier and found that they are a worthwhile and cost-effective method to deter traffic from crossing medians and into opposing lanes.


“For example, in 2007 we found that 95.1 percent of vehicles that hit cable barrier did not cross into opposing traffic lanes. (Also) cable barrier is designed to flex upon impact, which dramatically reduces the impact forces on errant vehicle occupants when compared to solid types of barrier.


“We also can treat more miles per dollar with cable barrier, and that difference can be significant. Depending on site conditions and other factors, we can treat 1.5 to 6.3 times the mileage with cable barrier than with other barrier, such as concrete.


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