Requirements for treating a curve

Curve warning treatment should be installed where:

• it is warranted by an advisory speed assessment survey (see Appendix A: Guidelines for the installation of curve warning and advisory speed signs);
  Appendix A: Guidelines for the installation of curve warning and advisory speed signs
  or
• a curve exists with a smaller radius than recommended for the posted speed (eg 80km/h curve on a road with a 100km/h operating speed), it may be expected to pose additional risk to drivers, and is considered geometrically substandard; or
• the advisory speed of the curve is at least 15km/h less than the 85th percentile speed on the immediately preceding section of the road. The advisory speed is defined as the maximum speed at which a curve may be comfortably negotiated under good road and weather conditions. (AS 1742.2–2009); or
• the crash history (actual or predicted) or other factors such as limited forward visibility, low levels of road surface friction, narrow sealed roads, shoulders and / or roadside hazards warrant additional treatments be considered. Predictions can be made using the KiwiRAP Road Assessment Tool (KAT) on state highways to determine high risk locations. Research undertaken in New Zealand (see High-risk rural roads guide 2011) has identified that the crashes/crash rate for curves increases as the difference increases between curve negotiation speed and the approach speed to the curve (typically estimated over the preceding 500m).
  High-risk rural roads guide