Wire Rope Safety Barriers
Wire rope safety barrier systems, also known as cable barriers, rely upon the tensile strength and deflection of wire cables to contain and redirect errant vehicles. Wire rope safety barriers are configured with four (4) cables supported by steel posts spaced every 2 m to 3 m. The posts are positioned within a plastic sleeve that is concreted into the ground facilitating removal of the damaged post following design impacts.
At each end of the wire rope safety barrier system the wire cables are tapered to ground level and secured to an anchor bracket that is concreted into the ground.
The deflection of wire rope safety barriers provides stable vehicle containment and low ride-down decelerations for vehicle occupants. Wire rope safety barriers are widely recognised for preventing dangerous head-on collisions on major highways and freeways.
Sentryline-M provides safe vehicle containment and redirection, utilising the tensile strength of tensioned wire rope cables supported by steel posts.
Frequently Asked Questions
How do cable barriers work?
Cable barriers rely upon the tensile strength and deflection of wire cables to contain and redirect errant vehicles. The cables are supported by posts which are typically positioned within plastic sleeves that are concreted into the ground. The posts are designed to yield by bending proximate to ground level when contacted by an errant vehicle.
What should a designer consider before specifying a wire rope barrier?
A wire rope barrier is classified as a flexible barrier and relies upon the deflection of the system to provide stable vehicle containment and redirection. Therefore, sufficient clearance behind these systems must be provided. In addition, the tensioned cables are not suitable for installation on tight horizontal curves as they may exert excess lateral force on the post foundations or readily dislodge from upstream and downstream posts during a vehicle collision causing a loss of system tension.
What are the MASH crash test guidelines for wire rope safety barriers?
- The length of the test section, including terminals shall be 183 m.
- The system should be tensioned to that specified for a temperature of 37.8 degrees which is typically the lowest specified cable tension.
These guidelines are intended to produce dynamic deflection results representative of real-life installations.
How do wire rope end terminals function?
A wire rope terminal is designed to anchor the tensioned cables. Crash testing is undertaken to ensure the tapering of the terminal does not cause vehicle snagging or rollover. A wire rope terminal does not absorb the kinetic energy of a vehicle impacting end-on and cannot be relied upon to bring the errant vehicle to a safe stop.
What is the advantage of using concrete post footings?
The lateral strength of the concrete footing should exceed the bending strength of the cable barrier post. This ensures the posts yield by bending proximate to ground level when impacted by an errant vehicle. The use of plastic voids within the concrete footing allows damaged posts to be removed and replaced following impact.
What is the maximum spacing between posts?
Australian state road agencies typically limit the spacing of cable barrier posts to 3 m centres.
What is the number or wire rope cables in the system?
Australian state road agencies require a minimum four cables per wire rope barrier system.
Can wire rope safety barriers be impacted from either side of the system?
Yes. This makes a wire rope safety barrier suitable for median applications where the crash barrier system may be impacted from either side.
Can wire rope barriers be connected to a guardrail barrier system?
No. Due to the differences in system stiffness a wire rope safety barrier cannot be directly connected to a guardrail barrier.
How should the overlap between a wire rope barrier and guardrail barrier be constructed?
The barriers should sufficiently overlap providing length-of-need continuity as per specific product guidelines. The lateral offset between the two barriers should be sufficient to accommodate the system dynamic deflection. Finally, the orientation of the overlap should prevent an oncoming vehicle from travelling behind the barrier systems.
