1.2.7 Determining rut depth using non-contact methods
Measurement of rutting by these non-contact automated technologies generally simulates one of two modes (Henry & Paterson 1994) as follows:
- straight edge model – an imaginary straight edge spanning high points across a wheel path. The results with this mode are sensitive to the length of the imaginary straight edge (see Figure 1.5)
- taut wire model – an imaginary stretched wire enveloping the high points across the whole lane profile (see Figure 1.5).
With the taut wire model, only the largest rut depth for the lane is usually reported, whereas the straight edge model can give a rut depth in each wheel path (wheel path rutting). The rut depth calculated by the taut wire model could differ substantially from the rut depth measured under a straight edge. For example, where the transverse profile is one large basin as illustrated by Profile A in Figure 1.5, the taut wire model gives larger rut depths than the straight edge model. In most cases, the taut wire model gives a more accurate indication of the potential depth of free water on the road surface.
Source: Austroads (2007d).