## 3 Methods for the Characterisation and Evaluation of the Skid Resistance of Asphalt Pavements  
### Characterisation Methods for Asphalt Pavement Macro- and Microtextures  
PIARC classified asphalt pavement textures into four categories based on wavelength and amplitude, as shown in Table 2. In practical engineering applications, the key factors affecting the slip resistance of pavements are macrotexture and macrotexture (Figure 4). In this context, microtexture is defined as being within the range of \(\lambda\) (wavelength) \(<\) 0.5 mm and A (amplitude) \(<\) 0.5 mm. The microtexture of pavements is primarily influenced by factors such as the shape, angularity, and textural properties of the aggregate particles [54, 55]. Macrotexture is defined as being around 50 mm in size, with a wavelength of between 0.5 mm and 50 mm and an amplitude of between 0.1 mm and 20 mm. The macrotexture observed in a pavement primarily depends on several factors, including the gradation, shape, and particle size of the mix [56]. An oversized texture in pavements is defined as ranging from 50 mm \(<\)\(\lambda\)\(<\) 500 mm to 0.1 mm \(<\) A \(<\) 50 mm, and the formation of the oversized texture mainly depends on pavement material, construction quality, construction \begin{table}
\begin{tabular}{p{71.1 pt} p{71.1 pt} p{71.1 pt}} \hline Asphalt Mix Type & Texture-Based Mix Category & Classification Details and Friction Characteristics [31] \\ \hline Hot Mix Asphalt & Continuous-graded asphalt mixture & Continuous-graded earthquakes earthquakes are made of continuous-graded, mutually embedded dense aggregates and asphalt in a hot mixing state; these mixtures form a hot paving state, and their macrotexture depths are generally 0.4-1.2 mm, but their microtextures are similar to open-graded and semi-open-graded asphalt mixtures [50]. \\ \hline Intermitt-graded asphalt mixture & Intermitt-graded asphalt mixture & Intermitt-graded asphalt mixtures consist of aggregates that lack one or more grades in the gradation composition and asphalt in the hot mixing and hot paving forming mix; their macrotexture depths are usually greater than 1 mm, and coarse aggregates creating a macrotexture are best, as they provide friction in wet weather and low tyre noise [51]. \\ \hline Open-graded asphalt mixture & Open-graded asphalt coarse aggregates, with fewer fine aggregates, and macroscopic texture depth ranges from 1.5 to 3 mm for mixes with residual voids greater than 15 percent after compaction, but the microscopic texture remains similar to that of other types of mixes [52]. \\ \hline Warm Mix Asphalt & Warm mix asphalt consists of aggregates mixed with asphalt at room temperature to form a mix that is environmentally friendly, with less dust and fumes, and exhibits very few differences between its macrotexture and microtexture compared to HMA pavements, and no significant differences in early skid resistance have been observed [53]. \\ \hline \end{tabular}
\end{table} 
Table 1: Salient details and frictional properties of asphalt mix classifications. technology, service environment, vehicle axle load, and other factors. Nevertheless, related studies have demonstrated that pavement texture can also be characterised by surface roughness, surface waviness, and shape error. Of these characteristics, surface roughness refers to the microgeometric shape of an object's surface, which is characterised by small spacings and peaks and valleys. This also belongs to the category of surface micro-shape. Surface roughness is different from surface macrotexture (e.g., straightness, roundness, etc.) and surface waviness. In the field of mechanical and friction research, surface roughness is usually divided by the size of the ratio of wave pitch (the distance between two neighbouring peaks or troughs) and wave height; a ratio of more than 1000 is a macrotexture, a ratio of less than 50 is a microtexture, and a ratio between 1000 and 50 is known as waviness.