Design Requirements

Number of Ropes - all Brifen barriers supplied in New Zealand use four cables, each one tensioned by Bridon personnel during initial installation to approx. 20kN, the exact tension depending upon ambient temperature at the time of installation.

The logic for using 4 cables is that they will always give lower deflection than a 3-cable system, all other factors being equal. Also, the ultimate strength of the system is obviously 33% greater with 4 cables rather than 3, which can make a critical difference in extreme impact conditions such as a fully laden truck.

So, all Brifen barriers in New Zealand always have 4 ropes whether they are TL3 or TL4. However, some other suppliers use 4 ropes for their TL4 system, but only 3 ropes for their TL3 barrier, despite the fact that TL3 barriers are just as likely to face extreme impact conditions such as fully laden trucks.

Dynamic Deflection - based upon crash testing to NCHRP 350 Test Levels 3 & 4 by independent, internationally renowned test facilities in the UK and USA, Brifen is approved by the NZTA for use in NZ as follows:

Other post spacing/deflection combinations may be used, but NZTA approval is required on a case by case basis.

Horizontal Curvature - installing wire rope barriers around curves can result in deflections being higher than the figures obtained from crash tests performed on straight sections. However, this can be countered by reducing post spacing around bends, and/or by the use of intermediate anchors on the apex of a bend.

Brifen's interwoven rope design makes it more tolerant of curvature than parallel rope systems, and curvature greater than 300m radius can generally be ignored. The angle through which the barrier curves is also relevant, for example a 90