To perform satisfactorily, safety barriers must have sufficient length to enable vehicle redirection. In addition, barrier end terminals require sufficient support to perform (absorb energy and anchor the system) as designed and tested.
When crash testing a barrier, MASH requires the minimum article length to be at least three times the length in which deformation is predicted, but not less than 30 m for steel beam systems and 180 m for wire rope safety barriers. The minimum barrier length does not include the length of end terminals.
Austroads sets the minimum length of road safety barriers (TL-3 in environments of speed >70km/h) as:
◼ 24 m for non-proprietary W-beam systems.
◼ 28 m for flexible W-beam systems.
These are the minimum lengths, you may require a longer barrier to shield the hazard based on either the angle of departure method or the run-out-length method (used in Victoria – see diagram below).
But as always, check your local supplements and guidance when designing barriers.