Roadside Safety - Barriers

Safety barriers are used to stop ‘out of control' vehicles from:

  • leaving the road and hitting roadside hazards, including slopes (roadside barriers)
  • crossing into the path of on-coming vehicles (see median barriers).

They are designed to redirect the vehicle and have a lower severity than the roadside hazard they protect. There are three main types of safety barrier (but within these types there are different systems which have their own specific performance characteristics).

Flexible barriers are made from wire rope supported between frangible posts. Flexible barriers may be the best option for minimizing injuries to vehicle occupants, however they may pose a risk to motorcyclists. These barriers deflect more than other barrier types and need to be repaired following impact to maintain their re-directive capability.

Semi-rigid barriers are usually made from steel beams or rails. These deflect less than flexible barriers and so they can be located closer to the hazard when space is limited. Depending on the impact these barriers may be able to redirect secondary impacts.

Rigid barriers are usually made of concrete and do not deflect. Rigid barriers should be used only where there is no room for deflection of a semi-rigid or flexible barrier. Rigid barriers are often utilized at high volume roadwork sites to protect road workers or other road users particularly where another barrier type is awaiting repair. Currently (depending on their height and other details) these provide the highest level of containment of heavy vehicles. In most cases following impact these barriers require little or no maintenance.

Much of the benefit from the use of barriers comes from a reduction in crash severity. Although a crash may still occur, it is likely to have a safer consequence than colliding with the object that the barrier is protecting.

  • If properly designed, installed and maintained, barriers should reduce the severity of crashes involving ‘out of control' vehicles.
  • When used in the median, safety barriers can greatly reduce the likelihood of head-on crashes.
  • A safety barrier should only be built if the existing hazard cannot be removed (see Roadside Safety - Hazard Removal).
  • The end points (terminals or end treatments) of barriers can be dangerous if not properly designed, constructed and maintained (see Related Images for examples of poor terminal treatments).
  • Safety barriers should be located so as to minimize high impact angles and should also allow space for vehicles to pull off the traffic lane.
  • Minor damage can reduce the safety benefits of barriers if they are not properly repaired.
  • Roadside barriers are a hazard to motorcyclists.
  • Ensure appropriate clearance behind safety barrier is considered particularly for flexible and semi-rigid barriers. With concrete barriers although they do not deflect, allowance must be made for any hazards taller than the barrier to be offset far enough from the face of the barrier so that during impact vehicles (particularly high vehicles such as trucks) do not lean over the barrier and strike the hazard.

Benefits

  • If properly designed, installed and maintained, barriers should reduce the severity of crashes involving ‘out of control' vehicles.
  • When used in the median, safety barriers can greatly reduce the likelihood of head-on crashes.

Implementation issues

  • A safety barrier should only be built if the existing hazard cannot be removed (see Roadside Safety - Hazard Removal).
  • The end points (terminals or end treatments) of barriers can be dangerous if not properly designed, constructed and maintained (see Related Images for examples of poor terminal treatments).
  • Safety barriers should be located so as to minimize high impact angles and should also allow space for vehicles to pull off the traffic lane.
  • Minor damage can reduce the safety benefits of barriers if they are not properly repaired.
  • Roadside barriers are a hazard to motorcyclists.
  • Ensure appropriate clearance behind safety barrier is considered particularly for flexible and semi-rigid barriers. With concrete barriers although they do not deflect, allowance must be made for any hazards taller than the barrier to be offset far enough from the face of the barrier so that during impact vehicles (particularly high vehicles such as trucks) do not lean over the barrier and strike the hazard.

Did you know?

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