High Tension Cable Barrier Systems

• As you know, high tension cable barrier systems are being installed iniiiiiiiii
  many areas of the state to prevent cross-over collisions. The Cable
  Safety System (CASS) is manufactured by Trinity Industries (
  http://www.highwayguardrail.com/products/cb.html ) and is being
  installed by Petersen Brothers. The tension of the cable varies with
  the ambient temperature, but it is safe to assume that it will be under
  approximately 5,000 to 8,000 pounds of tension.
  
  The new CASS system prevented two vehicles from crossing into oncoming
  lanes in the first month it was installed in Bellingham (
  http://www.wsdot.wa.gov/News/2006/06/8_CableMedianBarrier.htm ), and we
  have already had a collision where a vehicle was entangled in the
  cables. Responders did not cut the cable in that collision, but it
  raised a good question. What do we do if there are life threatening
  injuries and we can't get to the victims because of the cables. Can the
  cables be safely cut if necessary to save lives? Fortunately, the
  answer is yes, but only as a last resort.
  
  High tension cable barriers can withstand multiple vehicle strikes and
  still provide crossover protection, but when they are cut, at least
  1,000 feet of barrier is placed out-of-service until it can be repaired.
  For these reasons, WSDOT requests that emergency responders avoid
  cutting the cable whenever possible. However, as you will see in the
  attached videos, the cables can be safely cut in life threatening
  situations.
  
  With the assistance of Don Gripne of Trinity Industries, Peterson
  Brothers (contractor), and McLane Fire and Life Safety, WSDOT conducted
  a cable cutting demonstration on Highway 101 at Evergreen Parkway on
  January 18, 2007. We filmed three cable cuts using different cutting
  tools under several different tension loads to simulate real world cable
  strike situations. The cable tension meter is shown before the cut in
  each video, but the tension ranged from 8,260 lbs to 9,340 lbs.
  
  In Cut 1, the tension was 8, 260 pounds and the cut was made with a K-12
  circular saw between two undamaged posts. You will see that the cable
  retracted straight back about 15 feet to the posts. There was no
  whipping but there was significant unraveling of the strands, so it is
  important that the person doing the cutting be protected with heavy
  gloves. We also recommend that if a cable must be cut, that it be cut
  just far enough from the impact area to be able to cut between two
  undamaged posts.
  
• Video of Cut #1  (1,451 kb)
  
  In Cut 2, the tension was 9,340 pounds and the cut was made with a
  portable combi-cutter between two undamaged posts. Although it is not
  very visible until the end of this video, we used three to 4 wraps of
  duct tape on the left side of the firefighter to see if it would control
  the unraveling. If you look closely at the end of the video, you will
  notice that the cable on the left side of the firefighter had no
  unraveling whatsoever while the untreated cable to the right of the
  firefighter again had significant unraveling. Therefore, we strongly
  recommend that duct tape or some other form of tape be used before
  cutting to prevent unraveling.
  
• Video of Cut #2  (2,076 kb)
  
  In Cut 3, the tension was 8,300 pounds and the cut was made with a
  hydraulic cutter in an area without posts to simulate a situation where
  many posts have been knocked down. In this video, the cable was being
  pulled about 15 to 20 feet from the center of the median to simulate the
  stretching caused by a vehicle. Again, we always recommend cutting
  between two undamaged posts, but we wanted to demonstrate what would
  happen if the cable was cut in an area where the cable had been
  stretched and a number of posts were knocked down. In this cut, we
  wanted to test if the cable would whip back toward the center of the
  median because it was being stretched. As you will see, the result was
  very similar to the previous two cuts. We did not tape the ends, so you
  can see the unraveling, but there was absolutely none of the anticipated
  whipping action.
  
• Video of Cut #3  (1,764 kb)
  
  So in summary, here are our recommendations:
  
  1. Cutting the cables is a last resort and is only appropriate in
  life-threatening situations.
  
  2. If it is necessary to cut the cable(s), we recommend cutting between
  two(2) undamaged posts where the cables are parallel and not being subjected
  to multiple forces, and then cut only the minimum number of cables
  necessary.
  
  3. We recommend that the cable be securely taped with duct tape or other
  tape on each side of where it will be cut to prevent unraveling
  
  4. If the cables are tangled around a vehicle, lifting the cables out of
  the post may be appropriate. However, if you start to raise the cables
  and the post is lifted, stop and pull the post out of the way. Use
  extra caution and secure the post with a chain or restraining device as
  it may be under significant tension if the cables are twisted around a
  vehicle.
  
  5. Training is available from the manufacturer. To schedule training,
  contact Don Gripne, Trinity Industries, at (360) 943-9559 or via email
  at gripned@earthlink.net
  
  Please feel free to pass this information on to your local
  fire/rescue/recovery personnel.
  
  Thomas Dumont
  District 3 Traffic Engineer
  320-223-6540 (St. Cloud)

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