Frequently asked questions

  • A temporary safety barrier is defined as a road safety barrier that is installed in association with adjacent ongoing and continuous works, short term emergencies or similar situations. This type of safety barrier must be removed upon completion of the works or emergency. Temporary safety barriers perform in the same way as other road safety barriers however, the consequence of a failure of the barrier may involve injury to road workers.

  • Motorists are less likely to perceive roadside barriers as a hazard if the barrier is introduced gradually to the roadside environment through the use of a ‘flare’. Caution should be used in applying flaring as barriers are designed to work best with a glancing impact. Flaring may lead to vehicles impacting a barrier at a high angle that may lead to hazardous consequences. The flare rate should be designed in accordance with Austroads Guide to Road Design Part 6: Roadside Design, Safety and Barriers and any manufacturer’s specifications.

  • Yes. Safety barriers flared outside of the design clear zone still require an end treatment i.e. terminal, crash cushion to be attached.

  • In accordance with the requirements of Australian/New Zealand Standard AS/NZS 3845 there shall be no attachment to a road safety barrier system unless it can be shown by crash testing or by assessment that it is suitable.

    At present there are no road furniture items such as headlight screens, signs, lighting posts, fences, visual screens, debris screens etc. permitted to be attached to safety barrier systems.

    Screens may be placed adjacent to the side of the safety barrier not exposed to traffic. The distance between the screen and the product shall be determined by a site-specific risk assessment that considers the accepted deflection distance.

  • Surface pavement conditions should be smooth and free of snag points or obstructions that may interfere with the post impact vehicle trajectory and the operation of the product.

  • Safety barriers are often tested in strong foundations. To achieve the tested containment, equivalent foundation strength must be verified on site. If a weaker foundation is realised it is likely that as a minimum the safety barrier will have a greater deflection, if not fail, during impact. If the foundation type cannot be verified through geotechnical testing, it is recommended that a post pull-over test be conducted to validate the capacity of the foundation. Designers should refer to the Acceptance Conditions documents for permitted foundation conditions specific to individual safety barrier systems.

  • Safety barriers should be installed with sufficient distance to the hinge point to accommodate the barrier’s accepted dynamic deflection and to provide adequate lateral support for the system. This ensures that there is no damage to the batter following an impact and that the lateral support for the system is adequate to achieve the tested conditions.

    Where the site is constrained, it may be possible to place the barrier closer to or at the hinge point. Issues such as constructability, performance of the product, impact on posts/anchorage and space behind batter for workers need to be addressed. This may involve the use of longer posts or other treatments to ensure that there is sufficient lateral support for the barrier system. Maintenance of the barrier and the area behind the barrier may be difficult and appropriate maintenance procedures should be considered and documented as part of the installation requirements.

  • Appropriate clearance must be allowed between the safety barrier and the hazard that it is protecting to allow for either the accepted deflection or the working width of the barrier when impacted, dependent upon whether the hazard is above or below the road surface level.

    Where the hazard will not be impacted by any part of the vehicle that extends beyond the barrier, generally where the hazard is below road surface level (e.g. fill batter), the ‘accepted deflection’ is sufficient.

    Where the hazard may be impacted by any part of the vehicle that extends beyond the barrier, generally where the hazard is above road surface level, ‘working width’ shall be used.

  • The minimum distance between the back of the system and the edge of an excavation should provide sufficient distance to accommodate the barrier’s design deflection and provide adequate lateral support for the system, whichever is the greater requirement.

  • Safety Barrier systems with a legacy status continue to provide the level of service at which they were originally tested. Legacy status products may be maintained and/or repaired until the end of their service life or when parts are no longer available.

    It is recommended that when long lengths of legacy items are damaged, an assessment be made on whether an approved system may be installed instead.

    Relocation of legacy items is not permitted.

  • Yes. Safety barriers are not ‘see-through’ systems and will interfere with sight lines. This must be considered during the selection of the appropriate safety barrier system.

  • All safety barriers must have an approved connection or terminal attached at both the leading and trailing end. Only connections or terminals that are listed on the individual Acceptance Conditions documents are accepted for use. This ensures that an assessment of the proposed transition has been undertaken and that the suppliers of proprietary products are satisfied with the connection proposed.

  • When choosing a temporary safety barrier it is necessary to consider the speed environment during works and periods of in-activity. If it is likely higher speeds will be realised (or permitted) during periods of in-activity, a safety barrier approved for the higher speed zones is required. All equipment must be kept outside of the working width as a minimum.

  • Yes. However, where a safety barrier is installed in a median, the potential for the system to deflect into an opposing carriageway must be considered. The median width should allow full accepted deflection of the system without impacting the adjacent travel lanes.

  • It is not recommended that safety barriers be installed on a kerb as, upon vehicle impact, roll and pitch are developed which can affect the interaction of the vehicle with the barrier. This is more likely to occur where vehicle speeds exceed 70 km/h.

    Where installation on top of a kerb is required, the barrier should be offset either:

    • Far enough behind the kerb to allow an errant vehicle to stabilise after crossing the kerb before striking the barrier (desirably 1.5 metres), or
    • Close enough to the kerb so an impacting vehicle has not had adequate time to develop significant pitch and/or roll. It is important that enough offset from the kerb is provided for the foundation of the barrier to be constructed (desirably 200mm).
  • It has been demonstrated that the deflection of wire rope safety barrier will continually increase as the length of installation increases. It is therefore necessary to multiple the accepted deflection distances by correction factors to determine the appropriate design deflection for an installation. The correction factors are published in the Product Manuals for individual proprietary wire rope safety barrier products.

  • Wire rope safety barriers consist of tensioned ropes held between posts and, as such, there is a limit to their use on horizontal and vertical alignments.

    It is generally accepted that the minimum allowable horizontal curve radius for wire rope safety barrier installations is 200 metres, however if the supplier specifies a minimum that is different than this, the manufacturer’s requirements must be used.

    The minimum allowable sag curve K value is 30. The use of intermediate anchors at the base of sag curves may be considered to reduce ropes from rising. There is no K value limit for crest curves.

  • The maximum installation length of wire rope safety barrier between terminals is 1000 metres. Longer installations require intermediate anchorage. It is necessary to overlap the intermediate anchors to provide a continuous length of redirective barrier system. It is recommended that a minimum of accepted deflection distance is provided between the intermediate anchors. This minimises any risk associated with errant vehicles impacting two systems simultaneously which is not well understood at this time.

  • The unprotected motorcyclist is at great risk anytime he or she goes off the roadway at speed and contacts a barrier or any other object. Wire rope safety barriers pose a risk to motorcyclists generally because of their steel posts rather than the wire rope as commonly thought. The posts are designed to bend for vehicles, but not people, and generally, motorcyclists will come off their bike and slide under the wire or into a post. No direct evidence of increased injury from the ropes has been found.

  • Where necessary, to avoid an underground asset or similar, generally a single post may be omitted. In this instance the designer should contact the system manufacturer or the Standards & Technology team for assistance.

  • No. Safety barriers are tested to a standardised testing regime and undergo full technical and risk assessment by the Austroads Safety Barrier Assessment Panel prior to being recommended for acceptance. Redirective kerb would not pass these testing requirements.

  • A transition is required when connecting two different safety barrier systems together. This may be the connection of two different barrier types or the connection of an end treatment to a longitudinal barrier. The transition is used to accommodate any differences between the systems including differences in width, cross section, and stiffness. Transitions prevent ‘pocketing’ during vehicle impacts. Designers should refer to the Safety Barrier Acceptance Conditions for approved transitions.

  • End treatments are used to terminate and provide adequate anchorage to the longitudinal safety barrier. They are specifically designed to ensure that the ends of the safety barrier provide safe conditions for occupants of vehicles that may impact this area. End treatments are required at both the leading and trailing ends. There are different types of end treatments including crash cushions and terminals, both fulfil similar functions.

  • A run out area is required when a gating end treatment is used. A gating end treatment is designed to permit controlled penetration of errant vehicles behind the system. A run out area should be provided to allow adequate space for the vehicle to safely come to rest. Unless otherwise specified in the Acceptance Conditions documents, the run out area should be 18.5 metres in length x 6 metres in width (from the point of redirection) as defined in AS/NZS 3845.1 Road Safety Barrier Systems and Devices. Run out areas should have a crossfall of 10 to 1 or flatter and be free of roadside hazards.

    In urban areas it is recognised that the run out area can be difficult to achieve. Designers are required to undertake a risk assessment to determine any site specific issues associated with reducing the required run out area. If site specific issues cannot be mitigated then a fully re-directive crash cushion should be considered.

  • All safety barrier installations must have approved end terminals attached. For temporary installations on a divided carriageway the use of an approved but lower standard departure terminal may be considered. This will only be accepted when it can be clearly established that the likelihood of an approach impact is negligible and that any contra-flow is undertaken at low speed and under a traffic management plan.

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