## 2 Materials and Methods
### Experimental Design  
The retroreflectivity data used in this study were collected from three experimental test sites where the pavement markings were subjected to the real weather and traffic conditions. Test site 1, test site 2, and test site 3 were monitored from 2016-2017, 2018-2020, and 2020-2022, respectively. All the test sites were constructed at the same road section with the same characteristics and were subjected to similar climatic conditions. Figure 2 shows the toll plaza where the test sites were located. Experiments on highways require special attention because they involve several safety aspects. The experiment used the lines transversal to traffic as recommended by NTPEP [28]. This experimental setup presents the following advantages: all stripes can be placed close together in a short length of highway, which allows for the quick measurement of retroreflectivity; all materials are subjected to the same conditions of traffic and weather; and all the stripes are hit by vehicles, which accelerates the experiment. Although transversal stripes do not represent the real condition of markings, since they are applied longitudinally [5], transversal stripes provide similar results to overall pavement markings'  
Figure 1: Grain size distribution ranges of glass beads IIA and IIC from NBR 16184 (BRA) [21] and Type 2 and Type 3 from AASHTO M247 (USA) [22]. Figure 2: Experimental test site view [27]. degradation [29,30]. Figure 3a shows one example of the test site on the day of application and Figure 3b shows the stripes after being subjected to traffic for \(11\) months. Due to the high traffic volume of the highway, traffic interruptions for frequent retroreflectivity measurements would cause speed reductions and safety issues. Therefore, the test sites were constructed in a toll plaza rather than a free rolling section because drivers are aware and warned of a speed reduction, which avoids misunderstandings and safety issues. All the test sites were placed after the toll cabin and were subjected to the effect of vehicles' acceleration. The test sites were located on highway BR-381 (an important road in the southeastern region of Brazil with very heavy traffic of 2.27 \(\times\) 10\({}^{7}\) ESALs for a 10-year project). The traffic volume at this road section is approximately 17,000 vehicles/day, of which 35% are heavy vehicles. The retroreflectivity values were collected several times during the monitoring period and the intervals between the measurements were random due to limitations on traffic interruption or wet surfaces caused by rain. In case of rain, the data collection was rescheduled to at least 24 h after the rain ended. The measurements were collected only during the day on a dry surface with a portable retroreflectometer with 30 m geometry, as prescribed by ASTM E1710 [4]. The equipment measurement error was \(\pm\)5.0%, according to the manufacturer. The retroreflectivity was measured at the positions of the right and left wheel paths and the value considered herein is the average value between both readings for each stripe. These positions were selected due to their accelerated degradation since the retroreflectivity at the wheel path tends to present values around 50% lower than the center and edges [31]. Each experimental test site used different paints, glass beads, and glass bead application rates (ARs), which generated several material combinations, as shown in Figure 4. All the paints were applied with a wet thickness of 500 \(\upmu\)m, and no anti-skid was used. Test site 1 was constructed in July 2016 and the retroreflectivity data were collected for \(11\) months until June 2017. During this period, the retroreflectivity was measured 30 times, which generated over 6500 data points. The materials evaluated were two commercial paints, A and B, and two application rates of glass beads from three different manufacturers (\(\alpha\), \(\beta\), and \(\omega\)). This study used the gradations IIA and IIC from ABNT NBR 16184 [21] (Figure 1).