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Further to TAN #15-08: Road Safety Hardware Update-Temporary Concrete Barrier TCB-1, this Technical Advice Note clarifies issues related to the utilisation of concrete barriers to temporarily detain rockfall/slope debris. 

Concrete barriers have been widely used to detain rockfall and slope debris as a temporary measure whilst permanent solutions are sought. The concrete barriers used take a number of forms (New Jersey Barrier/Transit F-shape concrete barrier and other) and generally have been adopted for detention due to their no longer being compliant as temporary concrete road safety barriers. 

A number of operational and safety related issues have been experienced using such barriers for detention. Focusing on the Transport Agency’s adoption of Safe System thinking and focus on Zero Harm, the requirements for concrete barriers to temporarily detain rockfall/slope debris are detailed here. 

Requirements for concrete barriers used to temporarily detain rockfall/slope debris

Concrete barriers used to temporarily detain rockfall/slope debris shall comply with the following requirements:

• Reinforced to prevent spalling of concrete on the roadside face of the barrier following impact by rockfall/debris on the detention face;
• Appropriately faced on the traffic side to comply with concrete barrier requirements;
• Interconnected by an approved method to ensure individual barriers do not move when impacted by rockfall/slope debris or errant to traffic to create a road user hazard. It is expected that all new barriers will conform to the connection requirements of TAN#15-08. Existing barriers may be retrofitted with an acceptable linking system subject to RCA approval;
• Be in intimate contact with the ground along its entire base. No blocking or chocking of barriers is permitted;
• Located such that surface water drainage channels are not, as far as reasonably practicable, adversely blocked and that surface water is not deflected by the barrier on to the road or causes scour erosion;
• Located sufficiently behind any edge line to satisfy safety requirements as far as reasonably practicable as agreed with the RCA;
• Concrete barriers supporting fencing/netting or any other structure intended to control or limit rockfall/debris impact on to the highway, will require design to demonstrate that the concrete barrier does not adversely overturn under the impact loading due to the assessed 85th percentile rock/debris size. Such structures may be restrained to redress potential rotation;
• The requirements of CoPTTM.

Where compliance cannot be achieved a departure is required.

Application

This change shall take effect for new installations from 1 July 2016.

Existing temporary barriers shall be replaced as and when required through degradation, damage or impact.

All non-reinforced barriers shall be replaced no later than 1 July 2016, or as soon as reasonably practicable thereafter as agreed with the RCA.

Any concrete barriers/concrete barriers with associated fencing, intended as a permanent solution, will require detailed design and approval.

Improved inventory control

To facilitate inventory control, from 1 July 2016 all units shall be identifiable and a database of their date of manufacture and source, amount and location of reinforcing, condition, date of placement in current location and inspection dates shall be maintained.

Compliance checking

After 1 July 2016, the use of non-reinforced concrete barriers used to temporarily detain rockfall/slope debris will be considered non-compliant practice.

Further information

Contact Stuart Finlan of the Highways and Network Operations’ Structures team at stuart.finlan@nzta.govt.nz.

Kevin Reid