Isolated geometrically substandard curves (as identified using the guidance in Appendix A) should be signed as appropriate using the signs listed in curve treatments.
Appendix A: Guidelines for the installation of curve warning and advisory speed signs
Curve treatments
Two adjacent substandard curves
Where two geometrically substandard curves are in close proximity, the decision tree shown in Figure 3‑1 (below) can assist with the application of the sign layout strategy specified below:
Figure 3‑1
- sign curves independently with W12-1.1, W12-1.2, W12-1.3 or W12-1.4 signs displaying the curve advisory speed if:
- both curves warrant signing; and
- there is sufficient distance between the curves to install a sign on the approach to curve 2, i.e. the length of the tangent between the curves exceeds the distance given in Table 3‑5 (Location of advisory curve warning and speed advisory supplementary signs, and
Table 3‑5
- adequate clear visibility (120m in rural areas and 60m in urban areas) to the second sign can be achieved; and
- sign only curve 1 with a W12-1.1, W12-1.2, W12-1.3 or W12-1.4 sign displaying the curve advisory speed for curve 1 if:
- curve 2 does not warrant signing; or
- curve 1 has a lower curve advisory speed than curve 2 and both curves warrant signing but there is insufficient distance between the curves for separate signing; and
- where both curves have equal curve advisory speeds, both warrant signing and there is insufficient distance between the curves for separate signing, install a W12-2.1 or W12-2.2 Reverse Curve sign in advance of curve 1 displaying the common curve advisory speed; and
- where curve 1 has a greater curve advisory speed than curve 2, both curves warrant signing, and there is insufficient distance between the curves for separate signing, then install a W12-2.3 Reverse Curve sign displaying the curve advisory speed of curve 2 in advance of curve 1.
Figure 3‑1: Decision making tree for installing curve warning signs
Multiple geometrically substandard curves
Where a succession of three or more geometrically substandard curves of varying curve advisory speeds occurs over a section of road less than 1km in length, the curves warrant speed advisory supplementary signs, and there is insufficient distance for separate signing between the curves, then a W12-2.4 Reverse curves sign, displaying the curve advisory speed of the first curve, should be installed.
Where the section of road exceeds 1km in length, a W12-3.1 ‘Next "x" km’ supplementary plate should be used instead of a W12-2.4 Reverse curves sign.
Where two curves are in close proximity, plotting curve advisory speed values on an aerial photograph of the section of road under consideration will greatly assist in deciding the most appropriate configuration and combination of signs.
