# A Review of Long-Term Skid Resistance of Asphalt Pavement
## 2 Detection Method for Skid Resistance of Asphalt Pavement
### Indoor Asphalt Pavement Skld Resistance Detection Method  
AP skid resistance testing is susceptible to external factors. Indoor testing, on the other hand, has controllable variables and a shorter testing time. Compared to long-term on-site testing, it can play an important role in the design of the mix ratio, which in turn has important guiding significance and reference value for road maintenance [55, 56]. Many scholars mainly modify or develop rutting instruments, abrasion instruments, and other equipment independently to simulate the kneading effect of vehicle loads on the pavement in order to explore the skid resistance of AP [6, 7, 57, 58, 59]. Compared with the skid resistance test of outdoor AP, the indoor test is mainly to accelerate the wear test of the formed rutting plate or the core sample retrieved from outdoors. Through the detection of various skid resistance indexes, researchers simulate the decay of the skid resistance of the pavement under the actual driving conditions by point instead of surface [60, 61]. The classic abrasion equipment is shown in Figure 4, and the characteristics of different abrasion equipment are shown in Table 2. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Detection Methods**} & \multicolumn{3}{c}{**Characteristics**} \\ \cline{2-3}  & **Advantages** & **Disadvantages** \\ \hline \multirow{2}{*}{\begin{tabular}{c} Braking distance \\ method [49] \\ \end{tabular} } & It is the most direct method to determine the surface friction of the road surface & It has a narrow scope of application. The repeatability of test results is high. And traffic needs to be closed \\ \hline \multirow{4}{*}{\begin{tabular}{c} Smart sensor detection \\ method [35] \\ \end{tabular} } & Higher accuracy, easy to measure by automated operation, less human interference, does not affect the traffic, cost savings & Without considering the interactions among various weather conditions, relying solely on the information provided by the passive sensors on the intelligent pavement, and the less the actual data there are, the worse the detection effect will be \\ \hline \multirow{4}{*}{\begin{tabular}{c} Laser measurement \\ method [50, 51] \\ \end{tabular} } & It is difficult to achieve high-precision scanning of microstructures. Moreover, it cannot be used to measure pavements with numerous potholes and cracks, nor can it be used to measure waterlogged pavements. In addition, the equipment is relatively expensive \\ \hline \multirow{4}{*}{\begin{tabular}{c} CT scanning \\ systems [52, 53] \\ \end{tabular} } & It can provide high-resolution images, acquire three-dimensional data information of the road surface, and has high repeatability and stability & The test method can only scan the specimen indoors, and it is necessary to complete the preparation of AP specimen or drilling coring in advance \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Close-up \\ photogrammetry [54] \\ \end{tabular} } & Being able to collect high-precision AP texture in real time, and the measurements are highly accurate, efficient, and inexpensive & The texture information is uncontrollably lost \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Automated close-up \\ photogrammetric \\ systems [34] \\ \end{tabular} } & It has high acquisition efficiency and high measurement accuracy & It has high acquisition efficiency and high measurement accuracy \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Figure 4: Abrasion equipment. (**a**) Indoor accelerated abrasion tester [62]; (**b**) tire–pavement dynamic friction analyzer [57]; (**c**) MMLS3 accelerated loading tester [7]; (**d**) MLS11 accelerated loading tester [63]; (**e**) aggregate friction characterization tester [59]; (**f**) six-wheeled accelerated abrasion machine [64]; (**g**) multiple accelerated abrasion machinic (MAAM) [65]; (**h**) kneading machine [58]; (**i**) three-wheel polishing device [66].